MRI and RF compatible leads and related methods of operating and fabricating leads

ABSTRACT

RF/MRI compatible leads include at least one conductor that turns back on itself at least twice in a lengthwise direction, and can turn back on itself at least twice at multiple locations along its length. The at least one electrical lead can be configured so that the lead heats local tissue less than about 10 degrees Celsius (typically about 5 degrees Celsius or less) or does not heat local tissue when a patient is exposed to target RF frequencies at a peak input SAR of at least about 4 W/kg and/or a whole body average SAR of at least about 2 W/kg. Related devices and methods of fabricating leads are also described.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/047,602, filed. Mar. 13, 2006, which issued as U.S. Pat. No.9,492,651 on Nov. 15, 2016 and which claims the benefit of priority ofU.S. Provisional Application Ser. No. 60/895,619 filed Mar. 19, 2007,U.S. Provisional Application Ser. No. 60/912,835, filed Apr. 19, 2007,and U.S. Provisional Application Ser. No. 60/955,724, filed Aug. 14,2007, the contents of which are hereby incorporated by reference as ifrecited in full herein.

FIELD OF THE INVENTION

The present invention relates to conductors and leads and may beparticularly suitable for implantable medical leads.

BACKGROUND OF THE INVENTION

Linear leads comprising conductors can couple with radio frequency (RF)fields, such as those used in magnetic resonance imaging (MRI) andmagnetic resonance spectroscopy (MRS). Examples of such leads includeguidewires and/or interventional leads such as, for example, implantablepacemaker leads, spinal cord stimulator leads, deep brain stimulatorleads, electrophysiology or other cardiac leads, leads used forimplanted monitors, and leads used to administer a therapy during asurgical procedure. The coupling can sometimes result in local heatingof tissue adjacent the lead(s) due to RF power deposition during theMRI/MRS procedure, potentially leading to undesired tissue damage.

MRI is a non-invasive imaging modality with excellent soft tissuecontrast and functional imaging capabilities. However, MRI can be acontraindication for patients with implanted electrically conductingdevices and wires, including cardiac pacemakers and/or defibrillatorswith leads connecting implantable pulse generators (IPGs), deep brainstimulation (DBS) electrodes, spinal cord stimulators, physiologicalmonitors, etc. . . . , for several reasons. For example, the electronicsof the IPG/ICD may fail when in presence of the high magnetic fields, orthe RF used in MRI may damage the circuitry of the IPG/ICD. In addition,the implanted lead may couple to local electric fields induced in thebody during transmission of RF excitation pulses whereby the lead canunduly heat tissue adjacent the lead, or may propagate the RF toelectrodes at the distal end of the lead or to the device or IPG towhich it is connected, potentially causing local temperature rise tounsafe levels and/or damage to the implanted device. The heating problemhas been reported in the scientific literature by researchers.

For example, Luechinger et al. reported a local temperature rise of 20°C. in tissue adjacent to pacemaker leads implanted in pigs during an MRIscan. See, Luechinger et al. In vivo heating of pacemaker leads duringmagnetic resonance imaging, Eur Heart J 2005; 26(4):376-383. Inaddition, Rezai et al. reported in vitro tissue heating in excess of 20°C. adjacent to DBS (deep brain stimulation) leads during an MRI scan.Rezai et al., Is magnetic resonance imaging safe for patients withneurostimulation systems used for deep brain stimulation? Neurosurgery2005; 57(5):1056-1062. Even external leads such as those used formeasuring and monitoring physiological signals (electrocardiograms, EKG,electroencephalograms, blood pressure, sonography) during MRI may besubject to heating.

One approach to allow patients with implanted devices, such as IPGs andleads to be scanned by MRI, is the use of strictly controlled conditionsthat limits the input power of the MRI RF pulse sequences. This approachis reported by Gimbel et al., strategies for the safe magnetic resonanceimaging of pacemaker-dependent patients, Pacing Clin Electrophysiol2005; 28(10):1041-1046, and Roguin et al., Modern pacemaker andimplantable cardioverter/defibrillator systems can be magnetic resonanceimaging safe: in vitro and in vivo assessment of safety and function at1.5 T. Circulation 2004; 110(5):475-482.

In other (non-MRI) uses of RF, such as where external RF electromagnetic(EM) energy is present and/or used for therapeutic purposes, external orimplanted leads may also couple to the applied RF EM field and causeunsafe tissue heating or damage or destroy electronic devices that canbe connected thereto. For example, RF diathermy or ablation orcauterization of tissue can sometimes employ implanted or intra-bodyleads that may also couple to the applied RF EM field and cause unsafetissue heating, such as that reported for a patient undergoing RFdiathermy. See, Nutt et al., DBS and diathermy induces severe CNSdamage, Neurology 2001; 56:1384-1386; and Ruggera et at, In Vitroassessment of tissue heating near metallic medical implants by exposureto pulsed radio frequency diathermy, Physics in Medicine and Biology, 48(2003) 2919-2928. Another non-MRI example of where such EM-fieldcoupling may occur is where individuals with implanted leads are inclose proximity to EM field transmitters such as RADAR, TV, wirelesstelephone, radio facilities, fixed or mobile. Similarly, EM-coupling mayalso occur with external-conducting leads connecting electronicequipment that are sensitive to intense EM fields close to intense EMfield sources.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention are directed to RF/MRI compatibleleads and/or conductors. The leads and/or conductors are configured toinhibit, limit and/or prevent undesired heating of local tissue and/orthe propagation of RF to an attached electronic device by the leads whenexposed to certain levels of RF. Particular embodiments of the presentinvention are directed to flexible implantable leads with one ormultiple conductors that can be safely used in an external RF field,such as those used for MRI or MRS. The configuration of the conductor(s)can reduce unwanted coupling to RF-induced electric fields generated inthe body and may reduce, minimize and/or inhibit common modecurrent/voltage. The leads can be configured so that RF power depositionfrom the leads to adjacent tissue is reduced, permitting patientsimplanted with such leads, to benefit from MRI/MRS under saferconditions and/or permitting the use of elongate leads, cables and thelike to be used in magnet bores associated with MR Scanners during MRIprocedures.

Some embodiments are directed to RF/MRI compatible medical devices thatinclude an elongate electrical medical lead having at least oneconductor with opposing proximal and distal portions. The at least oneconductor turns back on itself at least twice so that it has a firstsection that extends in a first lengthwise direction for a firstphysical length, then turns to define at least one reverse section thatextends in a substantially opposing lengthwise direction for a secondphysical length, then turns again to define a third section that extendsin the first lengthwise direction for a third physical length. Thefirst, second and third physical lengths can be a minor sub-portion ofan overall length of the at least one conductor, and may include aplurality of sets of turns. In other embodiments, the conductor can beconfigured with a single set of longer turns forming the first, secondand third lengths may occupy substantially the entire length of theconductor.

The at least one electrical lead may be configured so that the leadheats local tissue less than about 10 degrees Celsius (typically about 5degrees Celsius or less) or does not heat local tissue when a patient isexposed to target RF frequencies at an input peak SAR of at least about4 W/kg and/or whole body average SAR of about 2 W/kg.

In some embodiments, the electrical lead heats local tissue less thanabout 2 degrees Celsius when exposed to target RF frequencies associatedwith MR Scanners at a peak input SAR of about 4 W/kg and/or whole bodyaverage SAR of about 2 W/kg. In particular embodiments, the electricallead can be configured to heat local tissue less than about 5 degreesCelsius when exposed to target RF frequencies associated with MRScanners generating a peak input SAR of between about 4-10 W/kg and/or awhole body average SAR of between about 2-5 W/kg.

Other embodiments are directed to MRI/RF compatible medical leadsystems. The lead systems include a lead comprising at least oneconductor. Each of the at least one conductors is configured with aplurality of (RF-induced) current suppression modules. The lead systemsalso include at least one electrode in communication with the at leastone conductor.

The medical lead system may be configured so that the reverse segmenthas a physical length that is shorter than that of the forward segment,and wherein the forward and reverse segments have an electrical lengththat is about λ/4 or less of an electromagnetic wavelength of interestof the at least one conductor in a target body.

The lead system may be configured to heat local tissue less than about10 degrees Celsius (typically about 5 degrees Celsius or less) whenexposed to RF associated with an MRI Scanner at a peak input SAR ofbetween about 4 W/kg to about 10 W/kg and/or a whole body average SAR ofbetween about 2 W/kg to about 5 W/kg.

Yet other embodiments are directed to medical leads that include: (a) atleast one electrode; and (b) a lead with at least one conductor incommunication with the at least one electrode. The at least oneconductor has a first forward portion that extends in a lengthwiseforward direction for a first physical distance toward the at least oneelectrode, then turns back at least once to define at least one rearwardportion that travels in a substantially opposing lengthwise rearwarddirection for a second physical distance, then turns back again todefine a second forward portion that extends in the forward direction athird physical distance with a distal portion of the second forwardportion residing beyond and downstream of the first forward portion.

In some embodiments, the second physical distance being less than thefirst and/or third physical distance. The first forward and firstrearward portions can have a substantially equal electrical length whenexposed to RF frequencies associated with an MRI Scanner.

Still other embodiments are directed to medical leads with at least oneconductor having spaced apart current suppression modules. At least oneof the current suppression modules comprising a length of conductorhaving a plurality of closely spaced conductor portions in a serpentineshape.

The serpentine shaped closely spaced conductor portions can includeconductor segments that extend in a lengthwise direction with bendportions therebetween that reside substantially within a substantiallycommon localized lengthwise extending region of the lead.

Additional embodiments are directed to MRI/RF safe lead systems thatinclude: (a) an elongate flexible lead with a plurality of conductorshaving a length with opposing proximal and distal end portions, theconductors each having a plurality of current suppression modulesextending along the length of the conductor, each current suppressionmodule comprising at least one coiled segment; and (b) a plurality ofelectrodes, one or more of the conductors in communication with arespective one of the electrodes.

The lead system may be configured to inhibit undesired temperature risein local tissue to less than about 10 degrees Celsius (typically about 5degrees Celsius or less) when exposed to RF frequencies associated withthe MRI scanner at a peak SAR input of between about 4 W/kg to at leastabout 10 W/kg and/or at a whole body average SAR of between about 2 W/kgto at least about 5 W/kg.

The lead system may be configured with corresponding pairs of theforward and rearward portions having substantially the same electricallength, and with the forward portions have a lengthwise physical lengthof between about 2-50 cm, and wherein the rearward portions have alengthwise physical length of between about 1-25 cm.

Yet other embodiments are directed to implantable flexible leads thathave a plurality of conductors extending between opposing proximal anddistal end portions of the lead. One or more of the conductors isconnected to at least one or a plurality of electrodes at the distal endportion thereof and at least some of the plurality of conductors areconfigured with at least one coiled conductor portion and at least oneclosely spaced serpentine shaped conductor portion.

The implantable flexible lead system may be configured so that at leastone of the conductors is configured so that at least some of theserpentine shaped portion resides inside the coiled portion of therespective conductor.

Some embodiments are directed to an implantable flexible lead thatincludes at least first and second conductors extending between opposingproximal and distal end portions of the lead. One or more of theconductors is connected to at least one of a plurality of electrodes atthe distal end portion thereof. The first and second conductors includea substantially straight portion and a coiled portion. The straightportion of the first conductor extends in a lengthwise direction outsideand proximate to the second conductor coiled portion or inside andthrough the second conductor coiled portion.

Yet other embodiments are directed to methods of fabricating a medicallead The methods include: (a) providing a length of at least oneelongate conductor; and (b) turning the at least one conductor back onitself at least twice to define two forward portions that extendlengthwise in a forward direction and at least one rearward portion thattravels in substantially opposing rearward direction for a secondlengthwise physical distance.

The methods may optionally also include, after the turning step, forminga flexible implantable lead body and sterilizing and packaging theimplantable lead body.

Still other embodiments are directed to lead systems with an elongateelectrical conductor adapted to reside in a patient with a first forwardextending segment having a corresponding first electrical and physicallength and a second reversed segment of the electrical conductor inclose proximity to the first segment and extending in a substantiallyopposing lengthwise direction from the first forward segment. The secondreversed segment has substantially the same or a shorter physical lengththan the first forward segment with substantially the same, less orgreater electrical length as the first forward segment when exposed toRF in the range of between about 1 MHz to at least about 200 MHz.

Additional embodiments are directed to methods of inhibiting heatinglocal tissue and/or suppressing or offsetting common mode RF currents inan electrical lead configured to reside in a patient, the electricallead comprising at least one conductor having a first forward sectionwith a first physical forward length and at least one reversed sectionextending in a substantially opposing lengthwise direction from thefirst forward section, the at least one reversed section has a secondphysical reverse length that is shorter than that of the first forwardsection and with an electrical length that is substantially the same orgreater than that of the first forward section. The method includes: (a)generating RF induced common mode current in the first forward sectionand the at least one reversed section of the electrical conductor,whereby common mode current flows in the first forward section and thereversed section in substantially the same direction; and (b) offsettingthe current in the first forward section and the reversed section at alocalized region of the conductor between the first forward and thereversed section.

The method may include placing the patient in an MRI scanner to carryout the generating step, then transmitting an electrical output to localtissue via an electrode in communication with the at least one conductorfirst forward and reverse sections thereby inhibiting the electrode fromunduly heating local tissue whereby the first forward and reversesections suppress common mode current propagated to the electrode by theelectrical lead.

Yet other embodiments are directed to lead systems adapted to connecttwo electronic devices and provide substantial immunity to signalsinduced by virtue of proximity to an electromagnetic radiation source.The lead systems include at least one elongate conductor having a firstelongate forward section that extends in a forward lengthwise directionfor a first forward physical length, then turns to define at least onereverse section that extends in a substantially opposing reverselengthwise direction for a reverse physical length, then turns again todefine another forward physical length. The at least one conductor isconfigured to be substantially immune (inhibit or not propagate) to RFinduced current and/or common mode signals induced by proximity to anelectromagnetic radiation source.

Yet other embodiments are directed to an RF compatible medical lead thatincludes at least one continuous length of conductor having at least onesegment with the lead configured to turn back on itself at least twicein a lengthwise direction.

Still other embodiments are directed to a conductive medical cable withat least one conductor configured for use in an MR Scanner bore, theconductor configured to turn back on itself at least twice in alengthwise direction to define an RF-induced heat resistant cable.

Other systems, devices, and/or methods according to embodiments of theinvention will be or become apparent to one with skill in the art uponreview of the following drawings and detailed description. Features orcomponents described with respect to one embodiment are not limited tothat embodiment and may be implemented into other embodiments. It isintended that all such additional systems, methods, and/or computerprogram products be included within this description, be within thescope of the present invention, and be protected by the accompanyingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will be more readilyunderstood from the following detailed description of exemplaryembodiments thereof when read in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic illustration of a phantom with a linear insulatedwire lead and electrode.

FIG. 2 is a graph of time (sec) versus temperature (C) at the electrodeshown in FIG. 1 based on a 4.5 W/kg peak input SAR MRI scan.

FIG. 3 is a schematic illustration of three different conductorconfigurations according to embodiments of the present invention.

FIG. 4 is a schematic illustration of two different lead configurationsaccording to embodiments of the present invention.

FIG. 5 is a schematic illustration of a single conductor having aforward and reverse segment according to embodiments of the presentinvention.

FIG. 6A is a schematic illustration of a single conductor having forwardand reverse segments that may be capacitively coupled according toembodiments of the present invention.

FIGS. 6B-6E are schematic illustrations of a conductor with a currentsuppression module of forward and reverse segments and exemplarycapacitance configurations according to embodiments of the presentinvention.

FIG. 7 is a schematic illustration of a lead with a conductor andelectrode, with the conductor having a plurality of forward and reversesegments spaced apart in a lengthwise direction according to embodimentsof the present invention.

FIGS. 8A-8C are graphs of temperature Celsius (C) change versus time(seconds) for different lead/conductor configurations (FIG. 8C is acontrol wire) according to embodiments of the present invention.

FIG. 9 is a schematic illustration of a lead with multiple closelyspaced conductors, the conductors having reverse and forward segmentsaccording to embodiments of the invention.

FIG. 10 is a schematic illustration of the lead shown in FIG. 9illustrating that the lead may also include capacitive coupling betweenthe reverse segment and one or more of the forward segments according toembodiments of the present invention.

FIG. 11 is a schematic illustration of a lead with multiple conductorsand multiple sensors and/or electrodes and multiple reverse and forwardsegments according to embodiments of the present invention.

FIG. 12A is a digital photograph of a prototype flexible lead accordingto embodiments of the present invention.

FIG. 12B is a partial view of the prototype shown in FIG. 12A with theend of the lead shown straight with respect to a ruler.

FIGS. 12C-12D are enlarged images of a portion of the lead shown in FIG.12B.

FIGS. 13A and 13B are graphs of temperature change (C) over time(seconds) for four electrode and four conductor lead systems accordingto embodiments of the present invention.

FIGS. 14A-14M are schematic illustrations of conductor configurationsaccording to embodiments of the present invention.

FIGS. 15A and 16 are graphs of impedance (Ohms) versus frequency (MHz)for some exemplary leads measured in saline according to someembodiments of the present invention (“CBS” in FIG. 16 means “coiledbackward section” and “CSM” means current suppression module).

FIG. 15B is a schematic of a measurement probe attachment configurationthat can be used to measure impedance such as the results shown in FIG.15A according to some embodiments of the present invention.

FIGS. 17 and 18 are graphs of temperature change (C) versus time(seconds) of exemplary leads in an MRI Scanner for a 1.5 T MRI scannerand a 3.0 T MRI scanner, respectively.

FIGS. 19 and 20 are graphs of impedance (Ohms) versus frequency (MHz) ofleads measured in various materials (saline, gel).

FIG. 21A is a schematic illustration of a single conductor with amulti-layer stacked coil configuration (tri-layer) of two forwardsegments connected by one reverse segment according to embodiments ofthe present invention.

FIGS. 21B and 21C are side views of stacked tri-layer conductorconfigurations. FIG. 21B illustrates a single conductor configurationand FIG. 21C illustrates two co-wound conductors according toembodiments of the present invention.

FIG. 21D is a partial side view of a proximal (or distal) end portion ofa lead according to embodiments of the present invention.

FIG. 22A is a schematic illustration of a single conductor with amulti-layer stacked coil configuration (two-layer) of two forwardsegments connected by one reverse segment according to embodiments ofthe present invention.

FIGS. 22B and 22C are side views of a two-layer stacked conductorconfigurations. FIG. 22B illustrates a single conductor two-layerstacked configuration and FIG. 22C illustrates two co-wound conductorswith a two-layer stacked configuration according to embodiments of thepresent invention.

FIG. 22D is a side view of a two-layer stacked two-conductor CSM leadconfiguration according to embodiments of the present invention.

FIG. 22E is a side view of the device shown in FIG. 22D with theaddition of a sleeve placed over the CSM according to embodiments of thepresent invention.

FIG. 22F is a partial exploded view of the device shown in FIG. 22Eillustrating a winding-direction transition zone where the lead goesfrom CW to CCW (or the reverse) according to embodiments of the presentinvention.

FIG. 23 is a schematic illustration of a lead with a conductor havingmultiple spaced apart segments of the multi-layered coils connected toan electrode according to embodiments of the present invention.

FIG. 24A is a graph of impedance (Ohms) versus frequency (MHz) of a leadhaving a plurality of spaced apart (in the lengthwise direction) threelayer current suppression modules (CSM) described in FIG. 21A.

FIG. 24B is a digital photograph of an exemplary method to measureimpedance of a current suppression module of a multi-conductorconfiguration according to some embodiments of the present invention.

FIGS. 25A and 25B are graphs of temperature change (C) versus time(seconds) of a 61 cm lead with two conductors and with two electrodes,each conductor having three-layer current suppression modules (about 12current suppression modules along its length) configured as described inFIG. 21A. FIG. 25A corresponds to the lead with the tri-layer CSMconfiguration and two electrodes in a gel phantom for the RF pulsesequence generating a peak input SAR of 4.3 W/kg in a 3 T MR Scanner.FIG. 25B corresponds to the lead in gel phantom in a 1.5 T MR Scanner ata peak SAR of 4.3 W/Kg.

FIG. 26 is a graph of impedance (Ohms) versus frequency (MHz) of a leadhaving spaced apart (in the lengthwise direction) two layer currentsuppression modules (CSMs) configured as described in FIG. 22A.

FIG. 27 is a graph of temperature change (C) versus time (seconds) of alead of about 61 cm with two conductors, each having about 12 two-layerstacked CSM segments having a length of about 5.7 cm. Thetemperature/time data was obtained for the lead in gel phantom in a 1.5T MR Scanner at an SAR of the pulse sequence of 4.3 W/Kg.

FIGS. 28A and 28B are schematic side sectional views of a conductor withmulti-layer coiled CSM configurations. FIG. 28A corresponds to the firstlayer of the single conductor of a two-layer (double stack)configuration such as that shown in FIG. 22A. FIG. 28B corresponds tothe three separate conductor layers of a three-layer configuration suchas shown in FIG. 21A.

FIGS. 29A and 29B are greatly enlarged digital photographs of a portionof a two conductor lead having a stacked (three layer) CSM configurationaccording to embodiments of the present invention. FIG. 29B alsoillustrates an outer layer on the lead to provide a substantiallyconstant outer diameter lead according to embodiments of the presentinvention.

FIGS. 29C and 29D are greatly enlarged digital photographs of a portionof a two conductor lead having a stacked (two layer) CSM configuration.FIG. 29D also illustrates an outer layer on the lead to provide asubstantially constant outer diameter lead according to embodiments ofthe present invention.

FIG. 30A is a schematic illustration of a DBS system with at least onelead, IPG and electrodes according to some embodiments of the presentinvention (the DBS system includes two leads and two IPGs).

FIGS. 30B and 30C are schematic illustrations of therapeutic systemswith leads in communication with a cardiac pulse generator. FIG. 30Billustrates the system can include two leads, extending to the RA andRV, respectively, while FIG. 30C illustrates that the cardiac system canhave three leads (one each in the RV, RA and LV).

FIG. 30D is a schematic illustration of a lead that connects twointernal or external devices according to embodiments of the presentinvention.

FIGS. 30E-30G are schematic illustrations of cables that extend within abore of an MR Scanner can be configured with the current suppressionmodules according to embodiments of the present invention.

FIGS. 31A, 31B, 32A and 32B are schematic illustrations of leads whichmay be particularly suitable for bradyarrhythmia and tachyarrhythmialead systems according to embodiments of the present invention.

FIG. 33 is a schematic illustration of a multi-conductor leadconfigurations according to some embodiments of the present invention.

FIGS. 34 and 35 are schematic illustrations of multi-conductor leadswith each conductor having multiple current suppression modulesaccording to some embodiments of the present invention.

FIG. 36 is a schematic illustration of yet another lead configurationwith stacked reverse and forward segments of adjacent lengths of asingle conductor forming a respective current suppression module andwith an RF trap shield layer according to embodiments of the presentinvention.

FIG. 37 is a schematic illustration of a lead with at least one innerconductor configured to rotate substantially freely with respect to thelead body according to embodiments of the present invention.

FIG. 38 is a schematic illustration of a lead similar to that shown inFIG. 37 but with the proximal electrode conductor comprising an RFtrap(s) along the length of the lead according to some embodiments ofthe present invention.

FIG. 39 is a schematic illustration of a lead comprising threeconductors with some cowound with others to form at least some currentsuppression modules for respective conductors according to someembodiments of the present invention.

FIG. 40 is a schematic illustration of a lead with multiple conductorshaving multiple respective current suppression modules spaced apartalong the length of the lead according to some embodiments of theinvention.

FIG. 41 is a schematic illustration of yet another lead configurationwith multiple conductors, each having current suppression modules, witha distal electrode conductor being substantially concentric to and/orinside the shock/stimulation electrode conductors according to someembodiments of the present invention.

FIG. 42 is a schematic illustration of another lead configuration wherethe distal electrode conductor comprises current suppression modules butone or more of the other conductors may be substantially straightaccording to embodiments of the present invention. As shown, the leadmay be particularly suitable as a passive fixation tachyarrhythmia lead.

FIG. 43 is a schematic illustration similar to FIG. 42, but with the endconfigured as an active fixation end according to embodiments of thepresent invention. This configuration may be particularly suitable as anactive fixation tachyarrhythmia lead.

FIG. 44 is a schematic illustration of another lead configuration withmultiple conductors where each conductor includes current suppressionmodules spaced apart along its length according to embodiments of thepresent invention. This lead configuration may be particularly suitableas an active fixation tachyarrhythmia lead.

FIGS. 45A-E are images of a winding sequence for fabricating a tri-layercurrent suppression module using a coil winder (shown with two cowoundconductors) according to some embodiments of the present invention.

FIGS. 46A-46F are images of a winding sequence for fabricating a twolayer current suppression module using a coil winder according to someembodiments of the present invention.

FIGS. 47A-47C are digital photographs of a subassembly of a lend withconductor having wound/stacked current suppression modules according toembodiments of the present invention.

FIGS. 48A-48D are digital images of a mold used to form the flexiblelead body of the wound conductor(s) shown in FIGS. 47A-47C according toembodiments of the present invention.

FIG. 49 is a digital image of a flexible lead with an overmolded outerlayer and the wound conductor(s) according to embodiments of the presentinvention.

FIG. 50 is a schematic illustration of an exemplary (and optional) moldwith a wound conductor subassembly therein according to embodiments ofthe present invention.

FIG. 51 is an end view of the subassembly and mold shown in FIG. 50.

FIG. 52 is a cutaway side view of the subassembly and mold shown in FIG.50.

FIG. 53 is a flow chart of operations that can be used to fabricate alead according to embodiments of the present invention.

FIG. 54A is a perspective view of an example of a test fixture used toassess fatigue resistance of some lead embodiments of the presentinvention.

FIG. 54B is a top view of the test fixture shown in FIG. 54A.

FIG. 54C is a digital photograph of a test fixture according toembodiments of the present invention.

FIG. 55A is a side view of a portion of a lead that may be suitable tobe a passive fixation pacemaker lead according to embodiments of thepresent invention.

FIG. 55B is a side perspective view of the lead shown in FIG. 55A.

FIG. 56A is a side view of a portion of a lead that may be suitable tobe a passive fixation ICD lead according to embodiments of the presentinvention.

FIG. 56B is a side perspective view of the lead shown in FIG. 56A.

FIG. 57A is a side view of a portion of a lead that may be suitable tobe an active fixation pacemaker lead according to embodiments of thepresent invention.

FIG. 57B is a side perspective view of the lead shown in FIG. 57A.

FIG. 58A is a side view of a portion of a lead that may be suitable tobe an active fixation ICD lead according to embodiments of the presentinvention.

FIG. 58B is a side perspective view of the lead shown in FIG. 58A.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout. It will be appreciated thatalthough discussed with respect to a certain embodiment, features oroperation can apply to others.

In the drawings, the thickness of lines, layers, features, componentsand/or regions may be exaggerated for clarity and broken linesillustrate optional features or operations, unless specified otherwise.In addition, the sequence of operations (or steps) is not limited to theorder presented in the claims unless specifically indicated otherwise.It will be understood that when a feature, such as a layer, region orsubstrate, is referred to as being “on” another feature or element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another feature or element, there are no intervening elementspresent. It will also be understood that, when a feature or element isreferred to as being “connected” or “coupled” to another feature orelement, it can be directly connected to the other element orintervening elements may be present. In contrast, when a feature orelement is referred to as being “directly connected” or “directlycoupled” to another element, there are no intervening elements present.Although described or shown with respect to one embodiment, the featuresso described or shown can apply to other embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis specification and should not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. As used herein, phrases such as “between X and Y” and“between about X and Y” should be interpreted to include X and Y. Asused herein, phrases such as “between about X and Y” mean “between aboutX and about Y.” As used herein, phrases such as “from about X to Y” mean“from about X to about Y.”

The term “lead” refers to an elongate assembly that includes one or moreconductors. The lead typically connects two spaced apart components,such as, for example, a power source and/or input at one end portion andan electrode and/or sensor at another position, such as at a distal endportion or electrodes at both end portions. The lead is typicallyflexible. The lead can be substantially tubular with a cylindricalshape, although other shapes may be used. The lead can have a solid orhollow body and may optionally include one or more lumens. In particularembodiments, a lead can be a relatively long implantable lead having aphysical length of greater than about 10 cm (up to, for example, 1 m oreven longer). The term “physical length” refers to a length that and canbe measured in units of length or distance, e.g., millimeters, inchesand the like, and is typically constant and does not vary when exposedto different electromagnetic fields (unlike electrical wavelengths),recognizing that a physical length may shrink or expand when exposed tolow or high temperatures. The lead can include at least one electrode,and in some embodiments, a plurality of electrodes (which may be both onproximal and distal end portions), and in some particular embodiments,at least one electrode can be a recording or sensing electrode or both arecording and stimulating and/or ablating electrode.

The term “conductor” and derivatives thereof refer to a conductivetrace, filar, wire, cable, flex circuit or other electrically conductivemember. A conductor may also be configured as a closely spaced bundle offilars or wires. The conductor can be a single continuous length. Theconductor can be formed with one or more of discrete filars, wires,cables, flex circuits, bifilars, quadrafilars or other filar or traceconfiguration, or by plating, etching, deposition, or other fabricationmethods for forming conductive electrical paths. The conductor can beinsulated. The conductor can also comprise any suitable MRI-compatible(and biocompatible) material such as, for example, MP35N drawn filledtubing with a silver core and an ETFE insulation on the drawn tubing.

The term “current suppression module” (“CSM”) refers to an elongateconductor that turns back on itself at least twice in a lengthwisedirection to form a conductor configuration of a reverse or backwardsection in one lengthwise direction and proximately located forwardsections that extend in the opposing lengthwise direction. The CSM canbe configured with a length that is a sub-length of the overall lengthof the conductor, e.g., less than a minor portion of the length of theconductor and the conductor can have multiple CSMs along its length. Theterm “MCSM” refers to a conductor that has multiple CSMs, typicallyarranged at different locations along at least some, typicallysubstantially all, of its length. The terms “backward”, “rearward” and“reverse” and derivatives thereof are used interchangeably herein torefer to a lengthwise or longitudinal direction that is substantiallyopposite a forward lengthwise or longitudinal direction. The words“sections”, “portions” and “segments” and derivatives thereof are alsoused interchangeably herein and refer to discrete sub-portions of aconductor or lead.

The term “MR compatible” means that the material is selected so as to benon-ferromagnetic and to not cause MR operational incompatibility, andmay also be selected so as not to cause undue artifacts in MR images.The term “RF safe” means that the device, lead or probe is configured tooperate within accepted heat-related safety limits when exposed tonormal RF signals associated with target (RF) frequencies such as thosefrequencies associated with conventional MRI systems or scanners.

The term “high impedance” means an impedance that is sufficiently highto reduce, inhibit, block and/or eliminate flow of RF-induced current ata target frequency range(s). The impedance has an associated resistanceand reactance as is well known to those of skill in the art. Someembodiments of the lead and/or conductors of the instant invention mayprovide an impedance of at least about 100 Ohms, typically between about400 Ohms to about 600 Ohms, such as between about 450 Ohms to about 500Ohms, while other embodiments provide an impedance of between about 500Ohms to about 1000 Ohms or higher.

Embodiments of the invention configure leads that are safe(heat-resistant) at frequencies associated with a plurality of differentconventional and future magnetic field strengths of MRI systems, such asat least two of 0.7 T, 1.0 T, 1.5 T, 2 T, 3 T, 7 T, 9 T, and the like,allow for safe use in those environments (future and reverse standardMRI Scanner system compatibility).

The term “tuned” with respect to a coil, means tuned to define a desiredminimal impedance at a certain frequency band(s) such as thoseassociated with one or more high-field MRI Scanner systems. When usedwith respect to a parallel resonant circuit with inductive andcapacitive characteristics defined by certain components andconfigurations, the word “tuned” means that the circuit has a highimpedance at one or more target frequencies or frequency bands,typically including one or more MRI operating frequencies.

The term “coiled segment” refers to a conductor (e.g., trace, wire orfilar) that has a coiled configuration. The coil may have revolutionsthat have a substantially constant diameter or a varying diameter orcombinations thereof. The term “co-wound segments” means that theaffected conductors can be substantially concentrically coiled at thesame or different radii, e.g., at the same layer or one above the other.The term “co-wound” is used to describe structure indicating that morethan one conductor resides closely spaced in the lead and is notlimiting to how the structure is formed (i.e., the coiled segments arenot required to be wound concurrently or together, but may be soformed).

The term “revolutions” refers to the course of a conductor as it rotatesabout its longitudinal/lengthwise extending center axis. A conductorwhere coiled, can have revolutions that have a substantially constant ora varying distance from its center axis or combinations of constant andvarying distances for revolutions thereof.

The term “serpentine” refers to a curvilinear shape of back and forthturns of a conductor as a subset of a length of the conductor, such as,for example, in an “s” or “z” like shape, including, but not limited toat least one flattened “s” or “z” like shape, including a connectedseries of “s” or “z” like shapes or with additional sub-portions of sameor other curvilinear shapes to define forward and backward sections of aconductor. The upper and lower (and any intermediate) lengthwiseextending segments of a serpentine shape may have substantially the sameor different physical lengths.

The term “Specific Absorption Rate” (SAR) is a measure of the rate atwhich RF energy is absorbed by the body when exposed to radio-frequencyelectromagnetic fields. The SAR is a function of input power associatedwith a particular RF input source and the object exposed to it, and istypically measured in units of Watts per kilogram (W/kg) taken overvolumes of 1 gram of tissue or averaged over ten grams of tissue or overthe entire sample volume, or over the volume of the exposed portion ofthe sample. SAR can be expressed as a peak input and/or whole bodyaverage value. Different MRI Scanners may measure peak SAR in differentways resulting in some variation as is well known to those of skill inthe art, while whole body average values are typically more consistentbetween different MR Scanner manufacturers.

Peak input SAR measurement is an estimate of the maximum input RF energydeposited in tissue during an MRI scan. To measure peak SAR, thefollowing methodology using a suitable phantom can be employed. The peakSAR temperature(s) is typically measured near the surface. The phantomcan be any shape, size and/or volume and is typically substantiallyfilled with a medium simulating tissue, e.g., the medium has electricalconductivity corresponding to that of tissue—typically between about0.1-1.0 siemens/meter. The medium can be a gel, slurry, or the like, asis well known, and has conduction and/or convective heat transfermechanisms. Peak input SAR is estimated based on temperature risemeasured by the sensors placed near the surface/sides of the phantom andis calculated by Equation 1 as stated below. See also, ASTM standardF2182-02A, which described a way to measure input SAR.dT/dt=SAR/C _(p)  Equation (1)

where: dT is the temperature rise

-   -   dt is the change in time    -   C_(p) is the constant pressure specific heat of water (approx.        4180 J/kg-° C.).

The tem′ “low DC resistance” refers to leads having less than about 1Ohm/cm, typically less than about 0.7 Ohm/cm, so, for example, a 60-70cm lead can have DC resistance that is less than 50 Ohms. In someembodiments, a lead that is 73 cm long can have a low DC resistance ofabout 49 Ohms. Low DC resistance can be particularly appropriate forleads that connect power sources to certain components, e.g., electrodesand IPGs for promoting low-power usage and/or longer battery life.

The lead can have good flexibility and high fatigue resistance to allowfor chronic implantation. For example, with respect to flexibility, thelead can easily bend over itself as shown in FIG. 49. In someembodiments, the lead, when held suspended in a medial location issufficiently flexible so that the opposing long segments drape or droopdown together (do not hold a specific configuration).

In some embodiments, the lead can be sufficiently fatigue resistant towithstand 1 million cycles of a degree of motion that includes axialrotation and lateral translation that is many times greater than thatimparted to the lead in position due to human anatomy/organ movement.The stroke cycle can be carried out at rates of between about 8-9 Hz(which is relatively fast compared to an average, resting humanheartbeat rate of about 1Hz). To be considered sufficiently fatigueresistant, a lead does not exhibit breakage, breakdown of insulation(insulation resistance breakdown or cracking, splitting or rupture ofinsulation) or short or open circuits when exposed to the test cycles.The leads can be tested submerged in a liquid (Normal saline) using atest fixture that automatically cycles a lead through a translationalstroke of about 2.9 inches. This stroke was selected to greatly exceednormal anatomical motions of the intended implant or use location of thelead (e.g., a cardiac cycle for cardiac leads) or respiratory cycle forleads that reside over the pulmonary region and the like. The lead canalso be configured to withstand rotation of about 180degrees/half-cycle.

An exemplary automated test fixture 350 is shown in FIG. 54A. The testfixture 350 includes a drive system 370 that can include a motor 370with a gear 372 that drives a belt or chain 371 that rotates wheel 380.A connecting rod 381 connects the wheel 380 to a linear slide block 393that linearly slides over table 395. The slide block 393 is alsoconnected to a rotational member 375 such as a gear assembly, e.g., arotating gear 390 in communication with a stationary rack gear 376(e.g., a rack and pinion gear assembly). In operation, the wheel 380rotates continuously which pulls the connecting rod and the connectedlinear slide back and forth causing the gear 390 to rotate thusimparting linear and rotational forces on the underlying lead 20.

The lead 20 can be attached to the fixture 350 using a holder such as alower extending rod 399 (e.g., a PEEK (poly ether-ether ketone) rod)that is held similar to an axle 391 in the center of the gear 390 andextends vertically down into a liquid bath (e.g., an end portion of thelead can be epoxied to or mechanically attached to the rod) so that thelinear translation and rotation motion of the stroke cycle generated bythe wheel 380 and rotation of gear 390 are directly imparted to the lead20. The movement is automatically carried out using the automated drivesystem 370 that automatically cycles the test specimen 20 repeatedly andcontinuously through a stroke cycle at a desired rate/frequency.

As shown in FIGS. 54A, the rod 390 is partially immersed in atemperature controlled, circulated water bath of Normal saline solution,while the lead 20 is completely immersed. The “free end” of the lead canoptionally be secured with a weight to confine the motion to a region orportion of the lead. The fixture 350 can provide discrete strokeadjustments in desired increments. The wheel 380 includes severalapertures 382 sized and configured to slidably receive mounting pin 383(FIG. 54C). The apertures 382 are radially offset at different distancesfrom the center of the wheel 380. By placing the connecting rod/crankpin 383 in a different aperture 382, the rod 381 and the slide block 393move a different linear distance through the rotation of the wheel 380.Also, the rack 376 is held at an adjustable location in slots 377 (FIG.54B). A different size diameter gear 390 (see, FIG. 54C, 390 a, b, c)can be placed on the slide block 393 and engage the stationary gear 376to rotate a lesser amount (a larger circumference) based on the linearmovement of the slide table 393. Thus, both linear and rotationalmovement is easily adjusted using this fixture 350. Two embodiments ofleads 20 with MCSMs formed of tri-layer stacked coils were tested withthis fixture and withstood over 2 million cycles and over 15 millioncycles, respectively.

As noted above, the leads may be particularly suitable for medical use,and can be used with interventional or other devices and may be acutelyplaced externally or in vivo or may be chronically implantable and caninclude one or more of a stimulating, ablating and/or recordingelectrode and/or sensor. The leads may be particularly suitable forimplantable lead systems for IPGs, cardiac defibrillators, cardiacpacing (CP), neurostimulation or neuromodulation (peripheral, deepbrain, or spinal), EP catheters, guidewires, SCS or any cable orconductors, particularly those that operate in an MR Scanner, and thelike.

The leads may be implantable, MRI compatible multi-purpose lead systemswith at least one stimulating/pacing electrode (in some embodiments withelectrodes at both end portions) and may optionally be configured toprovide an internal MRI receive antenna.

The leads may be particularly suitable as implantable or therapeuticdevices for animal and/or human subjects. Thus, the leads can besterilized and packaged for medical use. Some lead embodiments can besized and configured for brain stimulation, typically deep brainstimulation. Some probe embodiments can be configured to stimulate adesired region of the sympathetic nerve chain. Other embodiments may bedirected to other anatomical structures, organs or features includingthe heart. For example, the leads of the present invention may beconfigured for use in interventional procedures or as implantable leadsfor treating cardiac, gastrointestinal, urinary, spinal or other organsor body regions. In particular embodiments, the leads function asconventional pacemaker/ICD leads, i.e., leads that sense and transmitelectrophysiological signals to the pacemakers/ICDs and deliverstimulation pulse from the IPG/ICD to the cardiac tissue.

While the description below is directed primarily to medical uses, thescope of the invention is not intended to be limited thereto as, inother embodiments, the leads can be configured to connect two devicesand provide substantial immunity to (common mode signals induced byvirtue of proximity to) an electromagnetic radiation source and/orelectromagnetic fields having frequencies between about 1 MHz to atleast about 1 THz, typically between 1MHz and 1 GHz. The electromagneticradiation source can be from RADAR, communications transmission, e.g.,satellite or extra-territorial and territorial based cellular systems,television transmission, and/or radio transmission. The lead may be usedas an external non-medical device. The lead may also be configured forboth internal/external use or combinations thereof For example, the leadcan be configured as an implantable or interventional (acutely placed)medical lead that connects two internal devices, such as one or moreelectrodes to an IPG, a medical lead that connects one internal deviceto an external device (e.g., a therapeutic delivery device such to anexternal power source, control unit or supply), or an external medicallead that connects two external devices (such as a grounding pad to anRF generator for an EP (electrophysiology) ablation procedure).

Generally stated, embodiments of the invention are directed at single ormulti conductor leads where the conductor(s) of the lead are arranged soas to reduce RF pickup by the lead during exposure to electromagneticfields, such as, but not limited to, those associated with RF pulsesequences used with MRI Scanners. The conductors can be arranged inmultiple CSMs along the length of the lead. In some embodiments, theCSMs can be configured to have low impedance of between, for example,5-30 Ohms, while in other embodiments, the CSMs can have an impedance ofgreater than about 50 Ohms, e.g., an impedance of at least 100 Ohms,such as at least about 200 ohms, at MRI frequencies and the electricallength can be configured to be about or shorter than a quarterwavelength in a physiological medium in the electrical field. Thisconfiguration may significantly reduce coupling of the lead to the RFinduced in the body during an MRI scan, and propagation of the currentalong the length of the lead and into the tissue adjacent to anyassociated electrodes that the lead may optionally have.

During an MRI scan, the patient is placed in a constant magnetic field;external RF magnetic field pulses are applied to change the orientationof the nuclear magnetism and thus obtain signal from the sample: forexample, at 1.5 Tesla (T) this applied RF magnetic field has a frequencyof about 64 MHz. This field is perpendicular to the MRI scanner's staticmagnetic fields, and is linearly or circularly polarized. The RFmagnetic field can have associated with it an electric field, whosespatial distribution depends on the geometry of the MRI scanner'sexcitation coil and on the patient, but generally has the greatestamplitude closest to its conductors. The applied RF pulses can directlyinduce an electric field with an associated voltage and current in themetallic leads, implants (especially elongated ones) and conductors,consistent with Faraday's Law and Maxwell's equations, as is well knownto those skilled in the field of Electricity and Magnetism. Further, theapplied RF pulses generate local electric fields in the body that can beeffectively focused by the presence of metallic implants and electricalleads. In both cases, any voltages and currents that are induced in theconductors of the lead may cause them to resistively heat. Leads for usewith implanted devices, monitors and IPGs are typically designed for theconduction of direct current (DC) or audio frequency (AF) signals, andare typically electrically insulated along their length except forelectrode contacts. However, such DC/AF insulation typically provideslittle or no impediment to RF signals passing between tissues and theconductors, noting for instance that insulated wires are routinely usedon wires without affecting their ability to detect FM radio signals at81-108 MHz. Thus, it is conceivable that induced voltages and currentsinduced in such leads or implanted devices can be deposited in thetissue adjacent to the lead, electrode(s) and implanted devices. Incases where electrode(s) have small surface contact areas with tissue,and where the electrode is at a terminal end of a lead such that theinduced current and voltages are higher than on the rest of the lead,the contact tissue may present an increased risk of heating. Similarly,at terminal ends of leads that connect to implanted devices such asIPGs, excessive levels of induced currents and voltages may conceivablydamage the device.

Devices incorporating designs and arrangements of conducting implantableleads according to embodiments of the invention can significantlyameliorate sensitivity to induced RF currents and RF power depositionand/or other RF or MRI based heating phenomena. These arrangements canreduce the magnitude of the induced RF current and/or voltages, therebysuppressing to a significant extent the RF power deposited on and/orassociated with the lead, and consequently deposited in tissue adjacentto the lead (and electrode(s)). By this, the local temperature rise inthe tissue adjacent the lead and/or electrode(s) is reduced.

Typically, as exemplified for in vivo 1.5 T and 3 T MRI results herein,the lead is able to heat local tissue less than about 10 degrees Celsiusabove ambient or body temperature, more typically about 5 degreesCelsius or less, when a patient is exposed to target RF frequencies at apeak SAR of at least about 4 W/kg, typically up to at least about 20W/kg, and/or a whole body average SAR of at least about 2 W/kg,typically up to at least about 10 W/kg. In some embodiments, with a peakinput SAR of between about 4 W/kg to about 12 W/kg, the lead can inducea limited increase in temperature of less than about 6 degrees Celsius,typically about 5 degrees or less, with the temperature increase at apeak SAR of about 4.3 W/kg being less than about 2 degrees Celsius sothat a maximum temperature rise associated with the lead is less thanabout 2 degrees Celsius. In some embodiments, the lead is able to heatlocal tissue less than about 6 degrees Celsius when exposed to a peakSAR of between about 8 W/kg to about 12 W/kg, with the temperatureincrease at a peak SAR of about 8 W/kg and/or a whole body average SARof about 4 W/kg is typically less than about 4 degrees Celsius, and, insome embodiments can be below about 1 degree Celsius.

While not wishing to be bound to any particular theory of operation, itis contemplated that embodiments of the invention can employ one or morefunctional underlying mechanisms incorporated by arrangements ofconductors to thereby suppress and/or minimize RF coupling, inducedcurrents, and/or RF power deposition when implemented as external,implantable or intrabody leads subjected to RF EM fields. Thesesuppression mechanisms shall be discussed further below, in embodimentsof the invention detailed herein.

As noted above, the leads can be used in several situations whereindividuals who have external or implanted conductors and devices may beexposed to EM fields that could induce currents in them and therebypresent a safety concern or equipment malfunction, such as, for example,but not limited to, RADAR, radio, wireless (cellular) telephone orcommunications and TV transmission and receptioninstallations/facilities/equipment (fixed or mobile), RF devices, aswell as MRL Without limiting the intended scope of the currentinvention, for illustration purposes only, the description primarilydescribes embodiments of the invention in the context of exposure to RFin the context of medical MRI situations, such as, for example, duringan MRI guided interventional procedure or during MRI diagnostic imagingprocedures.

While not wishing to be bound to any particular theory of operation, itis currently believed that when a body such as a human or animal or abiologically analogous model object (“phantom”) is placed in an MRIscanner and an external RE magnetic field pulse is applied to the bodyto excite tissue for MRI during the scan, local electric fields (“Efields”) from the excitation coil and eddy currents can be induced inthe body. The magnetically induced eddy currents are in a directionorthogonal to the applied RF field and at the same frequency. Magneticflux may also be generated. When one or more conductors are placed inthe body, they can couple with the local E-fields and eddy currents canbe deposited on the conductors 2 of the lead 1 as shown in FIG. 1.Because the applied excitation fields will in general be substantiallyuniform over the cross-sectional dimension of the one or moreconductors, the coupled and induced currents in the conductors are inthe same direction, and shall henceforth be termed “common modecurrents”. This current travels back and forth at the RF, and can causea local temperature to rise to unsafe levels especially where currentspeak at the ends, in tissue adjacent to electrodes, for example as shownin FIGS. 1 and 2. FIG. 2 illustrates temperature rise on two differentleads, an SCS (spinal cord stimulation) lead and a DBS (deep brainstimulation) lead. The local temperature rise can be proportional to thetotal RF power deposited on the conductor, which is a function of: theapplied RF field strength, frequency and duty cycle; the electricallength of the conductor in the body, which is a function of theconductor's RF impedance (its conductivity, insulation thickness and thecomplex impedance of the environment around the conductor); and the sizeand RF electrical properties of the body.

In reference now to one theory of operation with respect to the commonmode currents, if two conductors (e.g., wires or filars) ofsubstantially equal or equal electrical length (the electrical lengthsand need not be the same as the respective physical lengths) are placedin the same electromagnetic (EM) fields in the same orientation, themagnitude and direction of current deposited on them will besubstantially the same or the same. Now, it will be seen, in accordancewith some embodiments of the present invention, that these conductorsmay be arranged in such a way so as to suppress (balance, offset, null,reduce and/or limit) the common mode currents by forming a conductorthat turns on itself two or more times, e.g., formed into sections thatinclude lengths whose direction is reversed in a longitudinal and/orlengthwise direction. By this configuration, it is contemplated that areduction or a cancellation of the common mode current in anelectrically equivalent forward length of conductor may be affected,thereby substantially reducing the overall current, which flows to theends of these conductors. However, it will be appreciated that with thisconcept, the conductor (e.g., wire) still traverses the distance fromone component to another, e.g. an electrode to an implanted device orIPG. In accordance with embodiments of the present invention, theelectrical length of reversed sections are modified so as to alter theirphysical length, while providing a canceling, nulling or offset affectof common mode currents. The lengths of the sections are chosen based onconsiderations described hereinbelow, which also include factors thatrelate the impedance and transmission line characteristics of theconductor, and/or its EM wavelength. The reverse sections can have aphysical length that is less or the same as at least one adjacent(neighboring) forward section and may have an electrical length that isless, the same or more than that of the at least one adjacent(neighboring) forward section.

Referring to FIG. 3, three different conductor configurations areillustrated. The top conductor 2 configuration is of a 27 cm longstraight conductor. When this configuration conductor was placed in asimulated tissue gel phantom and subjected to external RF fields in a1.5 T MRI scanner operating at about 64 MHz, a local temperature changeof about 20° C. was measured in the tissue adjacent to the electrode(see, FIG. 8C). In contrast, modifying the 27 cm conductor 2configuration as shown by conductor 3 with the conductor 3 turned uponitself (in about 9 cm sections) to define a conductor portion or segmenthaving a BS section 10 and two FS sections 9 causes a substantiallylower local temperature change, measured as less than about 1° C. duringthe same MRI scan carried out for conductor 2, which is similar to thatseen with a conductor 5 having a 9 cm conductor as shown by the bottomconductor configuration. Conductor 5 has a physical length of about 9 cmand may have an electrical length of about λ/4 or less. The temperaturereduction is believed to reflect reduced coupling to the local E-fieldsbecause of the reduced length of each section (9 cm vs. 27 cm). In thecontext of some particular embodiments of the invention, a common modecurrent may be induced in all three sections of the turned 27 cmconductor 3. However, again according to one contemplated theory ofoperation, the current in one forward section 9 ₁ of the conductor 3 maybe thought of as being canceled or reduced by the current in the reverse(backward) section 10, leaving a reduced (or net un-canceled) current inthe third (9 cm) section 9 ₂ consistent with this conductor 3 producingsubstantially the same heating as the shorter (9 cm) length conductor 5,alone. However, other or additional operational mechanisms may beresponsible for the reduced heating.

As shown schematically by the lead configuration in the middle of thethree leads in FIG. 3, reversing the direction of the conductor 3appears to offer an induced current suppression mechanism that ispotentially frequency non-specific and might be considered “broadband”suppression. However, in practice, several factors that are frequencydependent can be considered. In particular, at RF of about 30 MHz andhigher, the length of implanted leads can become comparable to the EMwavelength of current in the leads, which generally results inmodulation of the currents as a function of distance along the lead dueto the EM wave, which can cause any heating that occurs in the exposedsections (9 ₁, 9 ₂, and the like) to vary with position in response tovariations in the current amplitude, and can thereby modulate thecommon-mode suppression strategy outlined above.

Accordingly it may be desirable in some embodiments of the presentinvention to divide the long conductors used in lead systems into aplurality of individual RF-induced current suppression modules 8 thatare small compared to the wavelength. Thus, in some embodiments, eachindividual CSM 8 or a respective BS 10 and/or FS 9 thereof may have anelectrical length that is preferably no more than about λ/4, typicallyshorter than λ/4, where λ is the EM wavelength of the conductor in thebody at the RF of interest (e.g., the operational frequency of the MRIscanner). Generally stated, each module 8 has at least two sections, aforward section (FS) 9 and a backward section (BS) 10. The FS 9 and BS10 can have similar or substantially equal electrical lengths, and thusexperience a similar extent of coupling to the EM fields and similarmagnitudes and direction of induced common mode current when immersed inthe same EM fields. According to one common mode current suppressionmechanism theory, these similar magnitudes and directions of thecurrents induced in the forward and backward sections can be thought ofas meeting each other at the ends of each section, resulting in asubstantial cancellation of the current, as distinct from conventionalstraight leads wherein the current(s) can continue unabated and evenincrease, potentially causing undesired heating. Other non-equivalentelectrical length configurations may be used, for example, a shorterelectrical length in a FS 9 relative to a corresponding BS 10, and inthe location of the BS 10 on a proximal length, or on a distal length,relative to the overall physical length of the conductor 3 (e.g., wireor filar), and/or symmetrically disposed relative to a first turn orbend in the conductor 3.

The electrical length and wavelength (λ) of a conductor is a function ofits physical length, RF impedance, the insulator/dielectric materialsurrounding it and the electrical properties of the medium it is placedin. For example, at 64 MHz and in a saline solution (0.9%) a copper wireof the type used for winding magnetic coils (“magnet wire”) 9 cm long isroughly equal to λ/4. If insulation is added to the conductor, dependingon the insulation thickness and dielectric constant of the insulation, λincreases, i.e., the 9 cm long conductor with insulation now has anelectrical length that is shorter than λ/4. Also, coiling a length ofthe conductor can affect the effective physical and electrical lengths.The λ/4 length of the coil depends on the diameter of the conductor andthe diameter of the coil. For example, as shown in FIG. 4, a 9 cmstraight conductor (e.g., magnet wire) 9 is electrically equivalent inlength to a wire 10 having a 3.5 cm straight section 10 s and a 1.5 cmcoil 10 c formed of the conductor (e.g., magnet wire (diameter 0.040″ID)); and to a ˜2.5 cm of the same conductor (e.g., magnet wire) coiled10 c to an ID of 0.040″ (FIG. 9). FIG. 5 illustrates that the backwardsection 10 has a coiled section 10 c and an overall physical length“L_(CB)” of about 5 cm to provide substantially the same electricallength as the forward section 9, shown here with a linear (straight)length of about 9 cm.

As will be discussed further below, one or both of the FS 9 and/or BS 10segments of each or some CSMs 8 on a lead may each be coiled or comprisecoiled segments. According to embodiments of the present invention, inoperation, sections 9 and 10 are subjected to the same or a similar EMfield such that the common mode currents are induced in the samedirection, depicted here by arrows, will provide a certain level ofcancellation where the sections meet. It would appear that if sections 9and 10 are of electrically substantially equivalent lengths, and if theEM field is the same across the lengths of both sections, thencancellation should be complete. However, it is appreciated that, inpractice, current cancellation may not be 100% for various reasons,including for example variations in the coupling electric field in thetwo sections, but is sufficient to suppress common mode current(s) towithin acceptable limits. In vitro tissue heating tests of leadsconfigured as shown in FIG. 7 resulted in local temperature changes inthe gel surrounding the test lead of ˜1° C. as shown in FIGS. 8A and 8B.

In considering the mechanisms by which induced currents are amelioratedaccording to embodiments of the present invention, it will be recognizedin addition that the FS and BS portions 9, 10 of proposed currentsuppression modules 8 have RF electrical impedances comprised of thetotal resistance of the section, and a reactive component comprisedprimarily of the inductance of coil portions. It will be understood bythose skilled in the art that the term “coil” can include discretecircuit inductors (which are typically micro-wound coils; non-magneticand MRI-compatible for MRI applications) in addition to those coilsformed by the conducting leads.

In addition, the reactive component may include parallel capacitancedepicted as connecting between FSs 9 and BSs 10 and that is distributedmutually between lead sections or included as discrete components, aswell as stray capacitance between the surrounding environment in whichthe lead is placed, as illustrated in FIG. 6A. The distributedcapacitance may vary from being of negligible value to tens of pF.Discrete circuit elements (capacitances and/or inductors) may also beused in series in the lead in accordance with embodiments of the presentinvention. The reactance is a determinant of the EM wavelength in thesections, and their electrical lengths as discussed above. Thus, whenconsidering the impedance properties of the modules 8, the conductorarrangements of FS 9 and BS 10 as shown in FIG. 5, may potentially bethought of as adding the benefit of a high-impedance filtering effectwhen the magnitude of the impedance at the RF frequency of interest islarge, for example ≥100 Ohms. In general, this can occur over a range offrequencies, and in addition, higher levels of filtering can be expectedat certain specific frequencies where the conductor electrical lengthscorrespond to integral multiples of λ/4. While the latter property maybe limited to a relatively narrow RF range (“narrow-band” suppression),the RF filtering may be due to the impedance of the modules that istypical of that of inductor-capacitor (LC) circuits: the impedance at aparticular frequency is determined by the series inductance formedsubstantially by the coils incorporated into the sections, and by theparallel capacitance, which can arise between the conducting lead andthe adjoining environment, including nearby conductor portions (e.g., 9and 10).

Thus, when considering impedance effects, as exemplified in FIGS. 5,6A-6E, 9 and 10, the substantially straight sections 9 in conjunctionwith the BS coiled section 10 c may be thought of as forming an LCcircuit that provides an RF filter affect. As shown schematically inFIG. 6A, the coiled section 10 c can be an electrical equivalent of aseries inductor and a capacitance 7 that may be created by a (insulated)coil between the straight section 9 and the coiled section 10 c,insulated by a dielectric (e.g., a polymer), thus potentially creating ahigh impedance which suppresses induced RF currents. FIGS. 6B-6E areschematic illustrations of a conductor with a CSM 8 of forward andreverse segments 9, 10 and exemplary capacitance configurationsaccording to embodiments of the present invention. In these embodiments,the capacitance/capacitors are used in conjunction with the inductanceof the conductor (FIGS. 6B, 6C, 6D) or with one or more coiled sections(FIG. 6E) to reduce the physical length of the lead for a fixedelectrical length in order to suppress common mode currents and/or toprovide the a high impedance RF filtering effect. Note that of these,FIGS. 6C and 6D, may not be suitable for applications involving passageof direct currents (DC) or low frequency currents for pacemakers etc. .. . , due to the presence of the series capacitances. A purpose of theseries capacitances in FIGS. 6C and 6D, can be to augment the impedanceof a FS 9 to further improve the RF filter effect. The embodiment ofFIG. 6E includes a coil 9 c in FS 9 in addition to the one in BS 10.These coils are wound in opposite directions to each other, and may becowound with the FS conductor 9 next to the BS conductor 10 atsubstantially the same coil radius, or wound one on top of the other intwo or more layers, or consecutively coiled. A purpose of the added coil9 c can be to augment the impedance of a FS 9 to further improve the RFfilter effect, and may be of different length, diameter, and possess adifferent impedance from 10 c. Also, coil 9 c may be formed in either orboth of the upper and lower FS 9 portions. When using only a distributedcapacitance, FIG. 6E, may be accomplished just by forming conductor 3into FS coils 9 c and BS coils 10 c.

It will now be seen that these concepts and principles of embodimentsdescribed herein can be extended to embodiments including longer leads,multiple CSMs 8 with respective FS and BS sections 9, 10. One or more ofthe CSMs 8 can include BS sections 10 having coiled portions 10 c and FSsections 9 having coiled portions and leads 20 can include a pluralityof conductors 3, as depicted, and described in the examples presentedhereinbelow.

FIG. 7 depicts a prototype single lead system that has a length L₁ (suchas about 36 cm long) with a single electrode 4 showing four of six RFinduced current suppression modules 8 each with two FSs 9 with a lengthL₂ (such as about 9 cm long) corresponding to approximately λ/4 at 64MHz, and each with one with a BS 10 with a length L₃ (such as about 5cm) including a longer straight length L₄ (of about a 3.5 cm) and ashorter coiled length segment (of about a 1.5 cm) 10 c. In theembodiments shown, the conductor is formed from 0.007″ diameter magnetwire and the coiled sections 10 c have an inner diameter of 0.040″. Inconsidering the impedance of each suppression module 8, the coiled BS 10provides the inductance, and FS 9 couples with the inductor, with thestray capacitance contributed by the electrical coupling between the FSs9 and BSs 10 themselves and the environment. In considering the commonmode induced currents in each section, since both the respectivesections 9, 10 of the module 8 are in close proximity, they can coupleto substantially the same local E-fields and have substantially the samedirection of RF current induced in them at a given time, so that, inaccordance with the above discussion, the current deposited on theforward section 9 may be thought of as being cancelled to a significantextent by the current induced in the backward section 10 at the pointwhere the sections meet, and overall less induced current flows towardthe electrode 4 and into the adjacent tissues compared to that whichoccurs without CSMs 8.

The prototype shown in FIG. 7, underwent in vitro tissue heating testsin a 1.5 T MRI scanner operating at 64 MHz by placing it in an gelmedium having similar electrical properties as a healthy muscle(conductivity, 0.7 Siemens/m conductivity). Local temperature rise invarious sections (namely in gel adjacent to electrode 4) was measuredusing a fiberoptic temperature measurement system. FIG. 8A illustratesthe change in temperature (° C.) versus time (sec) for this lead in thegel at the electrode end, which is less than 0.5° C. In contrast, acontrol lead of a straight conductor of the same length in the samefield displayed a 20° C. temperature rise in the gel adjacent to theelectrode (FIG. 8C).

A 27 cm prototype was fabricated according to the design shown in FIG.7, but with a reduced number of modules 8 (four versus six) with thesame FS 9 and BS 10 configurations. FIG. 8B illustrates the in vitrotissue heat test data performed under the same conditions. The heatingat the electrode is slightly higher for the 27 cm lead, at about 1° C.,but remains within an acceptable range and greatly reduced compared tothe 20° C. seen in some conventional leads (FIG. 8C).

Another embodiment of a CSM 8 in accordance with the present inventionis shown in FIG. 9, which depicts a portion of the conductor 3 with asingle suppression module 8 that can be used to form a four-electrodeand/or four-conductor lead 20. In this case, each backward section 10has a coiled segment 10 c that runs substantially the entire lengththereof, for example, about 2.5 cm, rather than about 1.5 cm, as notedabove. Other lengths and coil diameters and coil sizes may also be used.As also shown, the four conductors or leads can be co-wound to providecowound coiled sections 10 c of sections 10 to counter the common modecurrents. Other configurations are possible including, for example,forming the coil 10 outside and surrounding the FSs 9 and BSs 10, suchthat each lead set reverses directions and runs back through the middleof the coil to its opposite ends to provide the cancellation effectdiscussed above. As shown in FIG. 10, from the standpoint of the RFimpedances of the lines, the coils 10 c may serve as series inductances,which, together with stray capacitance 7 with other sections 9 and/orsurrounding environment, provide a current suppression affect.

A multi-electrode, multi-conductor lead system 20 is illustrated in FIG.11 for a four electrode 4 and/or four conductor 3 lead system 20. FIG.11 illustrates a subset of the modules 8, e.g., five CSMs 8 of anexemplary 11 CSM conductors of a 58 cm lead 20, and five CSMs 8 of 12CSMs of conductors of a 64 cm lead system. For prototypes of the designshown in FIG. 11, each lead 20 was made with four conductors, namely0.005″ magnet wires (4 wires), each having a straight FS 9 about 9 cmlong, and a coiled BS 10 c (also interchangeably called a “CBS”) about4.3 cm long. The coils 10 c had a 0.046″ ID with respective coiledsegments 10 c of the different conductors being substantially co-wound.Multiple digital photographs of a prototype lead 20 for connectingbetween electrodes and an IPG or pacemaker are shown in FIGS. 12A-D: 12Athe entire lead; 12B the distal end showing the electrodes; 12C and 12D,close-up photographs of the modules 8 and coils 10 c. These leads 20were tested for in vitro tissue heating performance in a gel phantom ina 1.5 T (64 MHz) MRI scanner system. The local temperature changes inthe gel around different sections of the lead (distal end “DM1”,proximal end “PM1”, near electrode “electrode”) were measured and arereported in FIGS. 13A and 13B. Less than a 1° C. temperature rise wasrecorded in the gel adjacent to the lead 20 at these three locationswhen using an MM sequence having a peak SAR input of >4 W/kg.

While a four-electrode 4 containing four CSMs 8 is shown in FIG. 11,CSMs 8 for multi-conductor lead systems can typically comprise betweenabout 2-100 conductors 3 and/or electrodes 4, but even greater numbersof conductors 3 and/or electrodes 4 can be formed according to theembodiments described herein are included within the scope of thepresent invention.

In embodiments of the present invention, one or more such CSMs 8 of thetype illustrated in FIG. 11 for multiple conductors can be arranged sothat a CSM 8 of a respective conductor is separated from a neighboringCSM 8 by an electrical length of ˜λ/4 or less, analogous to the singleline arrangement depicted in FIG. 7, where λ is the EM wavelength of thestraight (uncoiled) lead in the medium in which it is to be implanted.Although shown as having electrodes 4 on both ends, in other embodimentsall electrodes may be at one end portion and connectors/interfaces tothe power source or other device at the other end. Alternatively,multi-electrode and/or multi-conductor (>2 conductor) embodiments of thepresent invention can include conductors having separate suppressionmodules as shown in FIG. 7. The multiple conductors 3 can be groupedwith the coil locations 10 c displaced one from the other so that thecoils 10 c do not coincide in space, and the maximum lead diameter doesnot become excessive. Combinations of cowound and non-cowound coiledsections and grouped or ungrouped conductors may also be used. In someembodiments, each coiled segment of a respective conductor can beaxially (displaced lengthwise) with respect to others, while in otherembodiments some or all of the conductors can be stacked one over theother and/or cowound.

The configuration details of the conductors 3 and CSMs 8 are forillustration purposes only and not meant to limit the scope of thepresent invention. While not wishing to be bound to one theory ofoperation, it is contemplated that the primary purpose of one or more ofthe cooperating pairs of forward and reverse sections, the coil sections9 c and/or 10 c, and/or the reactive elements depicted in FIG. 6A-E(coils and/or capacitors) is to alter the electrical length of theassociated conductor lengths so that common mode currents induced onlonger sections can be suppressed, offset or inhibited and an electricalconnection can be provided between physically separated parts, such aselectrodes and IPGs or pacemakers, or external EKG leads (or bloodpressure transducer, or blood oxygen transducer, or sonographytransducer) and a monitoring system, for example.

FIG. 12A is a digital photograph of a prototype flexible lead accordingto embodiments of the present invention. FIG. 12B is a partial view ofthe prototype shown in FIG. 12A with the end of the lead shown straightwith respect to a ruler. FIGS. 12C-12D are enlarged images of a portionof the lead shown in FIG. 12B.

FIGS. 13A and 13B are graphs of temperature change (C) over time(seconds) for four electrode and four conductor prototype lead systemsaccording to embodiments of the present invention. The graph in FIG. 13Aillustrates temperature rise over time at a distal end of a CSM module 1(DM1) and at a proximal end of CSM 1 (PM1) and in the gel near theelectrode if a 4 electrode lead system with 4 conductors and 11 CSMmodules having a length of about 58 cm. The graph in FIG. 13Billustrates the temperature rise of a 64 cm long prototype lead with 4conductors and 4 electrodes and 12 CSMs.

In particular, FIGS. 14A-14I illustrate exemplary CSM 8 configurationswith alternative conductor 3 configurations and BS 10 and FS 9 accordingto some embodiments of the present invention as applied to a singleconducting lead 3. In FIG. 14A, conductor 3 has BS 10 with a coiledsegment 10 c that runs substantially the entire length thereof analogousto the CSM shown in FIG. 9. FIG. 14B illustrates that one FS 9 mayextend inside the coil of a BS 10 to provide the cancellation effectdiscussed above. The FS 9 passing through the coil may pass through anyinterior portion of the coil, thereby generally resulting in a reductionin the outer diameter of the lead as compared to FIG. 14A, but alsoaffecting the RF impedance. This configuration is readily extended tomultiple co-wound leads, for example with respect to FIG. 9, by runningone bundle of leads FS 9 through the middle of co-wound coil 10 c, tominimize lead diameter. FIGS. 14C and 14D illustrate that a FS 9 canaxially loop or turn several times above, below and/or through a BS 10(defining several “mini” or “sub” FS 9 ₁, 9 ₂ and an intermediate “mini”BS 10 ₁) before extending axially downstream of the primary BS 10. Thelooping back and forth in this configuration provides an additionalmeans of altering the electrical length of the section in accordancewith the mechanisms of operation discussed above, thereby essentiallycreating a coil/inductance as in FIG. 14A, but with coil axis rotatedabout 90 degrees to augment coil 10. FIG. 14E illustrates that the FS 9can include a coiled segment 9 c and a linear segment 9 l, analogous toFIG. 6E. The coiled segment 9 c can reside proximate the BS 10 c. The BScoil 10 c and the FS coil 9 c can be substantially cowound but with eachcoil in opposing directions or coiled over or about one another orproximate each other to electrically couple, potentially produce currentcancellation at the end of the BS and may generate increased impedance,such as, for example at least about 100 Ohms, and typically about 300Ohms or more. The coil diameter, conductor size and/or type, and lengthof coil may be the same in the 9 c and 10 c sections, or one or more ofthese parameters may be different. The conductor 3 can be a singlecontinuous conductor along substantially its entire length, and istypically the same conductor at least along a length of a respective CSM8.

FIG. 14F illustrates that the conductor 3 can include a continuousclosely spaced section of conductor that turns on itself several timesin a lengthwise direction, analogous to the axial/lengthwise turns orloops introduced in embodiments FIGS. 14C and 14C. This configuration issimilar to that in FIG. 14A, except that the coil axis is rotated 90degrees, whereupon multiple BSs 10 are created by the coil windings.FIGS. 14G-14I illustrate yet other conductor CSM 8 configurations with aplurality of adjacent longitudinally extending back and forth lengths(which may be straight, taper or may be curvilinear) forming a series ofstacked reverse and forward segments 10, 9, respectively. Although notshown, one or more coils 3 c may extend between the adjacent CSMs 8,such as is shown in FIG. 14K (which also illustrates that the CSM 8 caninclude one double turn (one reverse segment) configuration. FIG. 14Jillustrates a configuration similar to FIG. 14K but without the coiledintermediate segment 3 c. Of course, the lead can include combinationsof different types and configurations of CSMs 8.

FIG. 14H illustrates that the modules 8 can include both the side(lengthwise) extending segments and a coiled segment with the sideextending segments being inside and/or outside the coiled segment andthe coiled segment can be a forward or a reverse segment, analogous toFIG. 14C. FIG. 14I illustrates that the side segments of adjacentmodules 8 in FIG. 14G, may be interleaved in part. In furtherembodiments, the interleaving of the conductor(s) is extended in whole,so that the axial and/or lengthwise loops are cowound and form a singlemodule. This can be obtained, for example, by forming a flat loop ofconductor at the center of module 8, then folding the loop several timesand laying it against the two FSs 9. An alternative embodiment is towrap the flat loop as a coil around a FS 9.

FIGS. 14L and 14M illustrate that the lead 20 can have at least oneconductor 3 at least one CSM 8 that extends between an electrode 4 and apower source, such as an IPG. FIG. 14M illustrates that the distal endof the conductor 3 can be coiled as it connects to the electrode 4 tofurther reduce heating proximate the electrode. Also, FIG. 14Lillustrates that more than one conductor 3 may be used to connect asingle electrode 4 for redundancy and/or lower power or energytransmission or the like.

FIG. 15A illustrates impedance versus frequency for a single CSM whenimmersed in a physiological saline solution. The CSM comprises 4.3 cmCoiled Back Sections (CBS) and 9 cm (straight) forward sections (FS).The CSM has 4 cowound conductors (for prototype proposes, magnet wires,0.005″ diameter) with the CBS having about a 0.046 inch inner diameter.FIG. 15B illustrates that the impedance can be measured by connectingthe impedance measurement probe to the CSM at the two points shown bythe arrows.

FIG. 16 illustrates impedance versus frequency for an entire lead witheleven axially spaced consecutive CSMs, when immersed in a physiologicalsaline solution. The lead is a 4 electrode system with FS having alength of about 9 cm and the CBS having a length of about 4.3 cm and aninner diameter of about 0.046 inches. The use of multiple CSMs may alterthe impedance dispersion in accordance with the cumulative impedance andwavelength effects associated with the longer lead length. The impedancedata shows very low resistance (˜1 ohm) at DC frequencies and around60-300 Ohm impedance at RF frequencies, although a peak of around 1600Ohm is evident at ˜20 MHz. Thus, the conductors 3 can have broadband lowpass filtering, while affording a higher impedance narrowband filteringeffect at specific frequencies.

Although the local maxima of the exemplary impedance is shown at betweenabout 20-25 MHz, the location and/or maxima impedance characteristicscan be adjusted to other desired RF frequencies by re-configuring theCSM, e.g., changing one or more of the length of the BS 10, the diameterof conductors defining the coil 10 c (e.g., inductors) and/or or part ofthe FS 9 c, and/or the number of revolutions on the conductors in thecoiled BS 10 c. Also, the leads 20 can be configured with multiple FSs 9and BSs 10, to generate maxima at multiple frequencies (or frequencybands) by adjusting the configuration, e.g., length/diameter/number ofrevolutions of different ones of the FSs 9 and/or BSs 10.

Thus, according to some embodiments, the conductors 3 with CSMs 8 canhave an impedance that varies and exhibits local maxima at a frequencyband and/or over a target frequency range. In some particularembodiments, the CSMs 8 can exhibit an impedance of at least about 100Ohms over its respective length at a target radio frequency of interest.The FS and BS sections 9, 10, respectively, can be configured such thatat least one local impedance maxima substantially coincides with atleast one frequency (or frequency band) of interest (e.g., 64 MHz for1.5 T, 128 MHz for 3 T, etc.) within that range. Because the localmaxima are relatively broad, the target frequency band can be within +/−about 5 MHz of the typical RF frequency of an MRI scanner. In someparticular embodiments, the target impedance local maxima can also bethe global maximum.

FIG. 17 shows heat-test data from the eleven-CSM lead whose geometry andimpedance properties are shown in FIG. 16 obtained using the MRIparameters: FSPGR sequence, TE=4.2, TR=17.3, BW=125, FA=170, 256=128image matrix; TG=155—peak input SAR˜4.2 W/Kg. FIG. 17 is a graph oflocal temperature change measured at different locations along thelength of the lead with eleven CSMs (corresponding FS and CBS) in a 1.5T MRI scanner operating at 64 MHz. The test method is as described withrespect to FIGS. 8A-8C.

FIG. 18 illustrates local temperature change measured at differentlocations along the length of a lead with eleven CSMs in a 3 T MRIscanner with measured peak input SAR=4.2 W/Kg. The MRI RF frequency inthis case is 128 MHz. The lead corresponds to that analyzed with respectto FIGS. 16 and 17, and the same test method as described for FIGS.8A-8C was used.

It is noted with reference to the eleven CSM lead depicted in FIGS.16-18, that impedance maxima in FIG. 16 do not exactly coincide with thetwo MRI frequencies of 64 and 128 MHz. Nevertheless FIGS. 17 and 18 showthat the leads are still highly effective at limiting heating at thehigher frequencies. This is consistent with the common mode mechanismplaying a significant role at the frequencies of interest. Also, thesame lead can be effective at limiting heating at two MRI scannerfrequencies, e.g., both at the 1.5 T frequency and at the 3 T frequency,and thereby potentially provide suppression of potentially injuriouslead heating and/or device damage in multiple MRI scanner and/or RFenvironments. In particular, the conductors 3 may provide for rejectionof induced voltages and currents over a broad band of RF in the rangebetween about 10 MHz to about 200 MHz. In some embodiments, the localmaximal can correspond to two or more RF frequencies of interest, whereone or more is an RF MRI frequency corresponding to 0.1, 0.3, 0.7, 1.0,1.5, 2.5, 3, 4, 4.7, 7, and 9.4 Tesla.

FIGS. 19 and 20 are graphs of impedance versus frequency (MHz). In thesegraphs, embodiment “B” refers to the embodiment shown in FIG. 14B,embodiment “C” refers to the embodiment shown in FIG. 14C and embodiment“D” refers to the embodiment shown in FIG. 14D. Each embodiment is ableto generate multiple local maximas over an RF frequency range (MHz) withEmbodiment C generating about 1000 Ohms at between about 70-80 MHz andgenerating over 200 Ohms between about 50-100 MHz. The word “flooded”means that there was no polymer layer on the conductor (magnet wire)CSMs so that the conductors are in complete contact with the surroundingmedium (saline or gel).

As shown, the conductors 3 can be configured to increase the impedanceand/or shift the frequency of local maxima of the impedance depending onthe length of the CSM (FS 9, BS 10, FS 9) and the orientation of the FS9 with respect to the coiled BS 10 c. In general, discrete ordistributed impedance elements such as inductors and/or capacitances,may be included in the leads for increasing impedance or tuning thelocal impedence maxima and providing desirable current suppressioncapabilities.

It is further noted that the conductors 3 and/or current suppressionmodules 8 may incorporate one or more of the above configurationsdescribed above and/or other features, such as, for example, but notlimited to, one or more of the following:

-   -   1) Thicker insulation on the FSs 9 as compared to the BSs 10.        Thicker insulation on the FSs 9 of the current suppression        module 8 may reduce the current deposited on FSs 9 and thereby        allow the length of the forward section to be increased.    -   2) In other embodiments, shielding of the conductor(s) 3 and/or        the lead FSs 9 can inhibit RF deposition and thus reduce the        current deposited on the FSs 9 as compared to no shielding.        Discrete or wound RF chokes as inductive elements, and/or        capacitive elements may be arranged between the shielding to        provide improved suppression capabilities. The shielding can be        continuous, discontinuous, or may be achieved by multiple        methods, to list a few, e.g., insulating conductors with        polymers filled with conducting metals doped for conductivity, a        braided covering and the like.    -   3) Making the FSs 9 physically longer than the BS 10, but        forming the FSs 9 to be electrically substantially equivalent or        of shorter length.    -   4) Different ones of the RF-current induced suppression modules        8 for a respective lead or a respective conductor can be        configured to have a different physical length and/or        configuration to provide a desired electrical length and RF        current suppression at a different operational frequency. For        example, for a multi-electrode system, some of the RF-current        induced suppression modules 8 thereof can be configured to        provide the λ/4 wavelength or less at a different MRI scanner        frequency than others, allowing for compatibility with different        high-fields, for future compatibility or backward compatibility.    -   5) The lead can be between 1 French to about 40 French. For        cardiac leads, the size can be between about 1 French to about        10 French. The lead and conductors may be flat or have a        geometric shape, tubular or otherwise. The lead is typically        flexible but can be configured to be substantially rigid.

In some embodiments, standing wave formation on long (coaxial)conductors may be attenuated by incorporating balun circuits or RFchokes at various locations on the longer FSs 9 or sections of the lead3 that extend between CSMs 8, or between electrodes or an electronicdevice and a CSM, or on a shield where this is included in embodimentsnoted above. See, Atalar et al., U.S. Pat. No. 6,284,971, entitled,Enhanced Safety Coaxial Cables, the contents of which is herebyincorporated by reference as if recited in full herein. See also, Laddet al., Reduction of resonant RF heating in intravascular cathetersusing coaxial chokes, Magn Reson Med 2000; 43(4): 615-619. See also, PCTApplication Serial No., PCT/US2005/028116, filed Aug. 9, 2005, entitled,Implantable MRI Compatible Stimulation Leads and Antennas and RelatedSystems and Methods, the contents of which are hereby incorporated byreference as if recited in full herein. Generally stated, thisco-pending application describes incorporating RF chokes on (DBS and CP)lead systems, and again would be applied in embodiments herein to thelonger FSs or portions of lead 3 that extend between CSMS, or betweenelectrodes or an electronic device and a CSM, or on a shield where thisis included as above.

Some physical and electrical parameters or characteristics of theconductor 3 and/or FS 9 and BS 10 with modules 8 incorporated in theleads 20 include:

-   -   1) Physical lengths of each current suppression module 8 of a        conductor between about 1 cm to 3 m long, but typically about 4        cm to about 10 cm.    -   2) Numbers of CSMs per conductor: typically between about 1-100,        and more typically between about 1-25.    -   3) Transverse spacing of each or some CSMs of a respective        conductor can be between about 0.1 mm to about 20 cm, and        typically between about 1 cm to about 9 cm.    -   4) RF impedance of a CSM can be any suitable value, from low        impedance to high impedance, such as above about 5 ohms,        typically >20 ohms, and in some embodiments about 100 Ohms or        greater along the length of a respective CSM at RF frequencies        of interest.    -   5) Overall RF impedance of the conductor and/or lead can be any        suitable value, but, in some embodiments, can be about ≥100        ohms.    -   6) Low DC resistance (allowing for lower power requirements        and/or longer battery life in some embodiments).    -   7) Cross-sectional width, typically diameter, of the        conductor(s): 0.0001 inches to about 0.5 inches, typically        between about 0.001 to about 0.2 inches, and more typically        between about 0.002 inches to about 0.1 inches. One or more of        the conductor(s) can be insulated and/or insulated and shielded.    -   8) The conductors may be circular, flat, rectangular, square or        elliptical or other shape in cross-section. The insulator, where        used, can be conformal so that when they are applied to the        conductor, does not change the shape.    -   9) The conductors can comprise any MR and biocompatible        material, including, for example, Au, Ag, Nitinol, Ti, Pt, Ir or        alloys thereof, MP35N, SST, DFT (drawn filled tube, typically        with a MP35N outer layer and a conductive (metallic) core such        as a silver core).    -   10) The conductors can be insulated by biocompatible materials        such as, for example, Teflon, Nylon, polymers, PTFE, ETFE,        silicone, polyurethane, PEEK (poly ether ethyl ketone), and/or        epoxy, which also act as dielectric material distributed between        the various conducting section in the leads.

FIGS. 21A, 21B, 21C and 22A, 22B, 22C are examples of leads 20 comprisedof stacked multi-layers 8 m forming the CSMs 8 of conductor 3. FIG. 23shows a lead 20 with at least one conductor 3 formed with a plurality ofCSMs 8 spaced apart in a lengthwise or longitudinal direction.

In particular, FIG. 21A illustrates a tri-layer configuration with threecoiled segments closely stacked over each other, with a first innerlayer coil 16 as a FS 9 c, an intermediate second layer coiled backsection 17 (10 c) and a third outer layer coiled forward section 18 (9c). FIG. 21B illustrates a single conductor triple stacked or tri-layerconfiguration 8 m while FIG. 21C illustrates a two conductor 3 ₁, 3 ₂,triple stacked configuration 8 m. As shown in FIGS. 21A-21C, the outercoil 18 and inner coil 16 can form two FS 9 (9 ₁, 9 ₂) and theintermediate coil 17 can be a BS 10. For leads with more than oneconductor 3 n (where n>1), two or more of the conductors 3 n can becowound to form the three layers, analogous to FIG. 9, as shown, forexample, in FIG. 21C which illustrates a two conductor 3 ₁, 3 ₂ stackedCSM configuration 8-2. For a three (or more layer configuration), thefirst layer 16 (8 i) can be wound from left to right (distal to proximalend of the lead), the second layer 17 (8 k) can be wound over the firstlayer and is wound right to left (from proximal to distal end of thelead), the final layer 18 (8 o) on the top of the two can be wound leftto right (distal to proximal end of the lead) and may have the same orsmaller (e.g., closer) pitch than the first two layers. In thisembodiment (stacked three-layer), all the layers 16, 17, 18 can becoiled maintaining the same rotation direction (CW or CCW) for the coilwinding equipment. A fourth or additional layers can be stacked on thethird layer 18 (not shown).

FIG. 21D illustrates a single conductor 3 in a tri-layer stackedconfiguration 16, 17, 18 (with each successive coil on a different butclosely abutting over layer) held about an integral flexible innersleeve 190, which may define an open lumen (not shown). As shown, atleast one end portion of the conductor 3 p (e.g., the proximal end) canbe configured so that the last or first CSM 8 merges into a wider pitchcoil 3 w for a number of revolutions, such as, for example, 3-10revolutions. As also shown, a relatively short outer sleeve 199 can beplaced over a portion of the CSM 8 as well as the coils 3 w to help holdthe conductor 3 in position/shape before the outer layer is placedthereon (e.g., by molding or other suitable method). The short outersleeve 199 length can vary, but in some embodiments can be between about0.5 cm to about 2 cm long.

FIGS. 22B and 22C also illustrate a two-layer multi-stacked CSM 8 m,with FIG. 22B illustrating a single conductor CSM 8 and FIG. 22Cillustrating a two conductor 3 ₁, 3 ₂ CSM 8-2. As shown, the inner layer8 i includes one FS 9 c and one BS 10 c, which reside under the other FS9 c formed as the outer CSM layer 8 o.

FIGS. 22D-22F illustrate a portion of a lead 20 with a two-conductor8-2, double stacked CSM 8. FIGS. 22D and 22F show the top layer 8 o insection view to illustrate the underlying layer 8 i of the pattern ofthe two conductors 3 ₁, 3 ₂. As shown in FIG. 22F, the conductors 3 ₁, 3₂ change rotational direction once at an end portion 33 of a respectiveCSM 8. FIG. 22E illustrates that a short length of a sleeve (such as aPET heat shrink tube) 199 can be placed over the end portion of the CSM33 at at least one end of the lead and a few revolutions of theconductors 3 ₁, 3 ₂ proximate thereto to hold the conductors in positionagainst the sleeve 190 and/or mandrel 190 m. In addition, a small amountof UV adhesive or other suitable adhesive (or other temporary orpermanent attachment means) can be placed on the conductors 3 ₁, 3 ₂and/or sleeve 190 at position 33 to help hold the conductors in positionprior to winding the next CSM 8. Other inner diameter sleeves/tubes canbe positioned at different locations to help hold the conductor(s) inposition, such as for attaching one or more electrodes/sensors ortransducers to the lead body (not shown).

In some embodiments, the leads are multi-conductor leads 20, such as,for example, but not limited to, leads having between about 2-100conductors 3, typically between about 2-50 conductors 3, and moretypically between about 3-16 conductors and some or all of theconductors 3 can be wound side-by-side in a substantially flat or levelfirst layer in a first direction (e.g., front to back or right to leftdirection).

In some embodiments, the co-wound conductors can then be wound to form asecond layer interleaved with and/or over the first layer, then wound toform at least a third layer (or even more layers), again with the thirdlayer interleaved with and/or above the first and/or second layer.Depending on the crossover of the conductors as the conductors 3transition to the different lengthwise directions, the second and thirdlayers (or additional layers where used) may have a varying diameter,but the layers may be substantially concentric with each other.

Each coil within a CSM 8 can have a different pitch or some or even allof the coils in a single CSM 8 can have substantially the same pitch. Insome embodiments, the first layer coil(s) can have a wider (lower) pitchand one or more of the overlying coil(s) can have a closer/more narrow(greater) pitch. Each layer of one or more coils of a respectiveconductor(s) can have a relatively thin thickness corresponding to thesize of the conductor (with insulation), such as between about 0.0001inches to about 0.2 inches. In some embodiments, each layer has athickness of about 0.001 inches to about 0.006, such as, for exampleabout 0.0026 inches, for a total thickness of the lead being less thanabout 0.20 inches (depending on the thickness of the outer encasementlayer), such as, for example, between about 0.015 to 0.020 inches.

The different closely spaced and/or stacked coiled sub-portions of asingle conductor 3 can be wound with the same or different pitches toform a CSM 8 and/or a CSM as well as the leading portion of the next,neighboring CSM 8 and/or a bridge to the next neighboring CSM 8.

In some particular embodiments, the different CSMs 8 of a respectiveconductor 3 can optionally be formed using multiple lengths of discreteconductors attached together, rather than a single continuous length ofconductor.

For a continuous length conductor, the windings can be substantiallycontinuous along a length of a respective conductor (or, where used,multiple conductors co-wound during the same winding set-up) and can beformed by substantially continuously or intermittently winding arespective conductor using an automated coil winder, such as, forexample, an Accuwinder Model 16B, available from Accuwinder EngineeringCo. having a place of business at San Dimas, Calif.

A lead incorporating multiple CSMs 8 (as illustrated in FIG. 23) wasprototyped and tested with two 0.007″ diameter 35N LT-DFT conductors(e.g., wires/filars) with silver core (19 filar cable, 0.005″ conductorOD and 0.001″ wall ETFE insulation), with the conductors (e.g.,wires/filars) cowound parallel to each other and coiled in three layers.The first layer (coiled forward section) has an inner diameter of0.023″, the second layer (coiled back section) is coiled over the firstand the third final layer (coiled forward section) is over the first andthe second layers. This CSM had an impedance of over 200 ohms at 64 MHzand length of 4.7 cm. The winding details are listed in Table 1 below.

TABLE 1 EXEMPLARY TRI-LAYER CSM Winding Direction of Layer # Directionrotation Pitch Length Layer #1 Left to Right Clockwise 0.050” 4.7 cmLayer #2 Right to left Clockwise 0.050” 4.7 cm Layer #3 Left to RightClockwise 0.020” 4.7 cmThe impedance of the 4.7 cm CSM section is shown in FIG. 24A. FIG. 24Bshows one example of a technique that can be used to measure impedanceof a multi-conductor configuration (the measurement may be different fordifferent CSM configurations). As shown, the measurement probe can beconnected to different conductors of the device, taking care to connectthe same conductor on each end of the device to be measured (e.g.,conductor 2 of 4) and connect this conductor to the measurement probeshield and core. The network analyzer can be calibrated to the end ofthe measurement probe and the impedance can be measured when loaded in asaline solution. A two conductor, 62 cm long lead, incorporating 12cowound trilayer CSMs 8 m along the length of the lead, was heat testedin 1.5 T (64 MHz) and 3 T (128 MHz) MRI scanners in an acrylamide gelphantom. The change in temperature (ΔT) in the gel (simulating tissue)adjacent to the electrodes as measured to be less than 2° C. with a 4.3W/kg peak input SAR, as shown in FIGS. 25A and 25B.

FIG. 22A is a two-layer coil stack configuration of a conductor 3 whereone or more conductors are wound/cowound in forward-back-forwardsections. As shown, two coils 16, 17 are on the same layer adjacent andinterleaved with each other and the other coil 18 resides over the innerlayer. Typically the BS 10 is coiled in the pitch of the first FS 9 ₁ onthe first layer and the second FS 9 ₂ is longer and extends over the BS10 and FS 9 ₁. The first forward and back sections 16 (9 c) and 17 (10c) are wound such that these do not overlap, and the back section 17 (10c) fits in the pitch (gap) of the forward section 16. This can be formedby attaching the proximal end of the conductors to a coiling mandrel orsleeve thereon and switching the rotational direction of the winding(left to right CW, right to left CCW, then left to right CCW or viceversa). The final forward section 18 (9 c) is coiled in the samedirection of the back section and over the first forward and backsection. The attaching can be adhesively and/or mechanically carriedout.

FIG. 22B illustrates a single conductor 3 configuration of a doublestack 8 m with both the inner coil FS 9 c and the BS coil 10 c beinginside the second layer 8 o with coil FS 9 c. FIG. 22C illustrates twoconductors 3 ₁, 3 ₂ coiled to form a two-conductor 8-2 double stack CSM8 m with the inner layer 8 i having both a FS and BS 9 c, 10 c,respectively, and the outer layer 8 o having a FS 9 c.

As discussed above with respect to FIG. 21D, FIGS. 22D-F alsoillustrates the optional flexible sleeve 190 (e.g., a biocompatibleflexible sleeve). The sleeve 190 is typically placed over the coilingmandrel during fabrication and can remain as an integral part of thelead 20 while the mandrel is typically removed. Other sized sleeves canbe used. The sleeve 190 outer diameter is typically sized to provide thedesired diameter of the lead (taking into account the outer diameter ofthe lead will also correspond to the number of stacked layers as well asthe outer over encasement or overlayer that defines a substantiallyconstant outer diameter). The sleeve 190 typically has a continuousclosed outer wall, but may be discontinuous and/or have open pores orapertures. In some embodiments, the sleeve 190 is biocompatible cancomprise any suitable material, typically a polymer such as PTFE orNylon (such as Vestamid® L2140), and can have any suitable size, suchas, but not limited to, an outer diameter of between about 0.01 inchesto about 0.1 inches, typically between about 0.01 to about 0.05 inches,more typically about 0.024 inches, a wall thickness of between about0.001 inches to about 0.02 inches, and can include a through lumen innerdiameter of between about 0.001 inches to about 0.025 inches, typicallybetween about 0.010 to about 0.02 inches, such as about 0.014 inches.The lead 20 can be configured so that the MCSMs extend substantially theentire length of the conductor as a series of continuous coils ofadjacent CSMs. The leads 20 can be connected to electrodes and bebipolar for some cardiac applications. A distal and/or proximal end ofthe lead may include a short length of straight or single layer coilthat connects to an electrode. To aid in maintaining coiled CSMs inposition or to inhibit unwinding/movement of a coil, a small piece orlength of heat-shrink tubing (e.g., about 10 mm or less of PET heatshrink tubing) can optionally be placed at different conductor coilsegments and heated to compress the conductor against the liner/mandrelto hold the conductor in position.

In addition, in some particular embodiments, the third layer can beformed so that most of the revolutions are at a tight pitch, e.g., 78revolutions at a pitch of about 0.2 in to end at a few last revolutions,e.g., 5-15 revolutions at a larger pitch such as about 0.7 in for easierelectrode installation/connection.

A lead 20 incorporating this FIG. 22A CSM 8 design was prototyped andtested with two 0.007″ diameter DFT conductors (with insulation), e.g.,wires/filars with silver core, 19 filar cable, 0.005″ cable OD and0.001″ wall ETFE insulation, with conductors cowound parallel to eachother and coiled in two layers. The first layer (coiled forward section)has an inner diameter of 0.023″ and a pitch of 0.05″, the second layer(coiled back section) is coiled in the space/pitch of the first layer;and the third final layer (coiled forward section) is on/over the firstand the second layers. This CSM had an impedance of over 200 ohms at 64MHz and length of between about 5 cm and 5.7 cm. The details of thewindings are as listed in Table II below.

TABLE II EXEMPLARY TWO-LAYER CSM Winding Direction of Layer # Directionrotation Pitch Length Comments Winding #1 Left to Right Clockwise 0.050”5.7 cm Layer #1 (CW) Winding #2 Right to left Counter 0.050” 5.7 cmLayer #1 Clockwise (CCW) Winding #3 Left to Right Counter 0.020” 5.7 cmLayer #2 Clockwise (CCW)To form the next adjacent CSM, the winding can continue in the CCWdirection (left to right) and the backward section can be coiled in theCW direction (right to left), followed by the other forward section alsoin the CW direction (left to right). That is, the conductor changes thecoiling rotation direction once per CSM and each adjacent CSM alternatesthe rotation direction of the different FS, BS, FS segments (e.g., CSMmodule one, CW, CCW, CCW, CSM module two, CCW, CW, CW, module 3, CW,CCW, CCW . . . ). As the conductor 3 exits the upper forward section itcontinues on to form the lower forward section of the next adjacent CSM8.

The electrical impedance of this 5.7 cm CSM 8 is shown in FIG. 26. Alead 62 cm long incorporating 11 CSMs 8 along the length of the lead 20(analogous to FIG. 23) was prototyped and tested. Heat test results fromthis lead show less than 2° C. temperature rise in the simulated tissue(gel) adjacent to the electrodes in 1.5 T field strength MRI scannerwith 4.3 W/kg peak input SAR (FIG. 27).

FIGS. 28A and 28B are schematic cross-sectional views of a conductor 3in the plane of its long axis with a multi-layer coiled CSMconfiguration 8 m. FIG. 28A corresponds to the first layer of atwo-layer configuration such as that shown in FIG. 22A. FIG. 28Bcorresponds to the three separate layers of a three-layer configurationsuch as shown in FIG. 21A.

FIGS. 29A and 29B are enlarged digital images of a multi-conductor lead20 having conductors 3 in substantially continuously arranged triplestacked layers of coils forming a CSM 8 m according to embodiments ofthe present invention. FIG. 29B illustrates an outer encasement layerthat defines a substantially constant outer diameter over the flexiblelead with the stacked CSMs 8 m. FIGS. 29C and 29D are digital images ofan enlarged multi-conductor lead 20 having conductors 3 in substantiallycontinuously arranged double stacked layers of coils forming a CSM 8 maccording to embodiments of the present invention. FIG. 29D illustratesan outer encasement layer that defines a substantially constant outerdiameter over the flexible lead with the stacked CSMs 8 m.

The exemplary coil diameters, coil lengths, and conductor lengths canhave a significant range of values within the scope of the invention,typically with a primary design parameter being that of wavelength notedabove. While embodiments of the invention have been illustrated in thecontext of MRI exposure at 64 MHz (1.5 T MRI) and 128 MHz (3 T MRI), itis intended that applications of the present invention to MRI shallinclude MRI over the full range of RF afforded by MRI scanners,including, for example, 0.1, 0.3, 0.7, 1.0, 1.5, 2.5, 3, 4, 4.7, 7 and9.4 Tesla (T) systems, especially commercially available scanners suchas, 1.5 T scanners, 3 T scanners (128 MHz), 1 T scanners (42 MHz), 0.5 Tscanners (21 MHz), 4 T (170 MHz) and 7 T (300 MHz) scanners.

It is also contemplated and included in the present invention thatembodiments involving implanted leads include the use of biocompatiblematerials and/or coatings, and the conductors 3 include aluminum, gold,silver, platinum, rhodium, iridium, rare earth metals, alloys of theseand other conducting metals including Nickel Titanium alloys (e.g.,nitinol, MP35N, etc.), and conductors formed from coatings of metals,for example, gold coated nitinol, or nitinol or MP35N, etc. with asilver or Pt core, etc., such as, for example drawn tubing forming ofMP35N available from Ft. Wayne Industries located in Ft. Wayne, Ind.,USA.

For implantable leads 20, the designs can be configured to have themechano-chemical properties of flexibility, strength, durability,resistance to fatigue, non-corrodible, non-toxic, non-absorbent, andbio-compatible and/or bio-inert. It is further contemplated thatembodiments of the invention can be used in any of a range ofapplications where implanted conducting leads (or external orcombinations of same) are required, including but not limited to:connections to IPGs, DBS electrodes, cardiac pacemakers, cardiacelectrodes, nerve stimulators, electrodes, EEG and EKG monitors (deviceswith either or both internal and external leads), cardiacdefibrillators, power sources and/or control lines for artificial limbs,power sources and/or control lines for artificial organs (kidneys, etc);power sources and/or control lines for implanted bio-substrates orenzyme delivery devices (e.g., insulin delivery) or other drug deliverydevices, and the like.

FIG. 30A is a schematic illustration of a DBS system with at least onelead (typically two leads) with CSMs 8 and an IPG and electrodes 4according to some embodiments of the present invention. Optionally, asshown in FIG. 30A, the proximal portion of the lead 20 e can bereinforced and/or larger (thicker) than the distal portion. This largerportion 20 e can be integral on a single lead or may be provided as amatable/connecting lead extension. The proximal end portion 20 e canhave a length of between about 2-15 cm, typically between about 5-10 cm.The larger portion/extension 20 e can provide increased fatigue ortorque resistance or other structural reinforcement proximate a rigidbody, such as, for example, an IPG. The proximal portion or leadextension 20 e can include one or more CSMs 8 or may not include anyCSMs 8. Alternatively, the lead extension 20 e may include a differentlyconfigured CSM 8 and/or a less dense CSM arrangement (less CSMs per cm)relative to the distal portion of the lead 20. FIGS. 30B and 30C areschematic illustrations of therapeutic systems (medical devices) withleads connected to a cardiac pulse generator. FIG. 30B illustrates thesystem can include two leads, extending to the right auricle (RA) andright ventricle (RV), respectively, while FIG. 30C illustrates that thecardiac system can have three leads (one each in the RV, RA and leftventricle, LV). FIG. 30B also illustrates that the distal end portion ofthe lead 20 e may have a larger (thicker) and/or reinforcedconfiguration relative to the more flexible distal end portion asdiscussed with respect to FIG. 30A. Again, the proximal end 20 e canhave a length between about 2-15 cm, typically between about 5-10 cm.

FIG. 30D schematically illustrates that the lead system 20 interconnectstwo electronic devices 50 ₁, 50 ₂ residing either inside or external toa human or animal body. In some embodiments, the devices can benon-medical devices, such as communication devices. In other embodimentsthe devices can be medical devices. For example, at least one endportion of the at least one conductor 3 connects an electrocardiographicelectrode 50 ₁ and at least another end is connected to anelectrocardiographic monitoring device 50 ₂. In other embodiments, atleast one end portion of the at least one conductor 3 is connected to anelectroencephalographic graphic electrode 50 ₁ and at least another endis connected to an electroencephalographic monitoring device 50 ₂. Instill other embodiments, at least one end portion of the at least oneconductor 3 is connected to a blood pressure monitoring transducer 50 ₁and at least another end is connected to a blood pressure monitoringdevice 50 ₂. In yet other embodiments, at least one end portion of theat least one conductor 3 is connected to a blood oxygen monitoringtransducer 50 ₁ and at least another end is connected to a blood oxygenmonitoring device 50 ₂.

FIG. 30E is a schematic illustration of an MR Scanner 500 with ahigh-field magnet bore 500 b. In some embodiments, the lead 20 can beconfigured to extend inside the bore 500 b during some interventional ordiagnostic procedures. The lead 20 can be a cable, extension or guidethat manipulates a device such as a robotic or remotely operated tool orother device. The lead 20 can connect an external control unit 50 ₁ toan adjustable or moveable component or tool 50 ₂ inside the magnet bore500 b. The lead 20 can be torqueable, e.g., rotate to turn or manipulateinput or surgical devices or tools. The lead 20 can include at least onecable or conductor with at least one CSM 8 with a respective at leastone FS and BS 9, 10. FIG. 30F illustrates that the tool 50 ₂ can be anadjustable trajectory frameless head mount 510 that can be used toadjust the trajectory of the implantable lead to place and implant DBSleads using MR guidance while the patient remains in the magnet bore 500b. FIG. 30G is an example of one surgical tool, a frameless head mount510, with cables or leads 20 configured with at least one CSM 8according to embodiments of the present invention.

Described below are exemplary designs that can be implemented on anylead, including, for example, cardiac leads, such as bradyarrhythmia andtachyarrhythmia or ICD lead systems. Although shown with electrodes, theconfigurations can be used with other elements or with just a lead orcable, as appropriate to the application. The RF/MRI safe leads 20 caninclude one or more conductors 3 of the lead arranged in multiple CSMs 8where each CSM has a length of between about 1.5 cm to about 6 cm, andeach CSM 8 is arranged such that it has impedance exceeding about 100ohms at target MRI frequencies (for example, 128 and 64 MHz).

FIGS. 31A, 31B, 32A and 32B are schematic illustrations of leads thatare described as particularly suitable for bradyarrhythmia andtachyarrhythmia or ICD lead systems, for which it is desirable to renderMRI-safe and/or RF safe, according to embodiments of the presentinvention These leads and/or features thereof can be modified to fitother applications as well. The leads 20 may include different tissuefixation configurations such as, for example, passive fixation or activefixation. In passive fixation the distal end of the lead is anchored inthe folds of the cardiac tissue. In active fixation, the distal end ofthe lead is a helical screw, which is fixed in the cardiac tissue.

Bradyarrhythmia leads or pacemaker leads (FIG. 31A, 31B) typically havetwo electrodes 4, a distal pacing and sensing electrode 31, and theproximal ground electrode 33. The conductors 3 connecting the distalelectrodes 31 and 33 to IPG contact electrodes 35 and 36, are typicallycowound/coiled along the length of the lead 20. In passive fixationleads, the distal electrode 31 may be a conductive contact; whereas inactive fixation leads this contact can be a helical screw 37 which canbe torqued and turned by turning the proximal end of the coiledconductor via electrode 36.

Tachyarrhythmia leads (FIGS. 32A and 32B) typically have threeelectrodes; distal pacing and sensing electrode 31, and two proximalshocking electrodes 38 and 40. The conductor 3 connecting the distalelectrode is coiled along the length of the lead, and is in the centerof the lead. The shocking coils are cowound coils of non-insulatedconductors, and are connected to the proximal electrodes/IPG byconductors 39 and 41.

Now in accordance with embodiments of the present invention, conductingleads of the tachyarrhythmia, bradyarrhythmia, ICD (implantablecardio-defibrillator) and/or pacing lead system may be formed with CSMs8 or with CSMs and shield elements to suppress induced RF currents andimprove the safety of such devices during MRI, as exemplified in FIGS.33-44 and FIGS. 55A-58B. Thus, FIG. 33 illustrates a lead 20 with apassive fixation bradyarrhythmia lead design with two conductors 3 ₁, 3₂, each conductor is wound in CSMs 8 and arranged along the length ofthe lead one conductor 3 ₁, alternating the other 3 ₂. Each conductorhas CSMs 8 formed along the length and spaced intermittently. When thelead is assembled, the CSMs of each conductor are interleaved/alternatedalong the length of the lead. The straight sections of the conductorswill typically overlap the CSMs of other conductors. Conductors 3 ₂ and3 ₁ connecting to the distal electrode 4 and distal ground electrode 31,respectively, are wound in CSMs 8 which are spaced apart from eachother. When the lead 20 is assembled, the CSMs 8 of the two conductors 3₁, 3 ₂, alternate.

FIGS. 34 and 35 show embodiments with two conductors 3 ₁, 3 ₂, withmultiple CSMs 8 along the length of the lead 20; with one conductor 3 ₁CSM assembly substantially concentric to the other 3 ₂. The CSMs 8 ofthe conductors 3 ₁, 3 ₂, have inner and outer diameters such that theycan be concentrically arranged along the length of the lead. Oneconductor CSM assembly, for conductor 3 ₂ can rotate with respect to theother, i.e. in CSM assembly for conductor 3 ₁. The CSMs 8 of theconductors 3 ₂ and 3 ₁ have inner and outer diameters such that they canbe concentrically arranged along the length of the lead. One conductor 8CSM 3 ₂ assembly can rotate with respect to the other 3 ₁. The centerconductor CSM assembly 32 is connected to the fixation helix 37 at thedistal end. The fixation helix 37 can be manipulated by torquing thecenter conductor CSM assembly 3 ₂ and this in turn rotates and laterallyslides the fixation helix 37 in and out of the lead 20 allowinganchoring in the cardiac tissue.

FIG. 36 shows a passive fixation bradyarrhythmia lead embodiment withdistal electrode conductor 3 wound in trilayer CSMs 8 m along the lengthof the lead and is in the center of the lead 20. The proximal connecteris connected to the IPG by means of a RF high impedance shield layer 48with RF traps 49 and the shield layer can shield the inner conductor 3and CSM 8 m thereof. The conductor 3 ₁ connecting to the distalelectrode may be arranged along the length to have one or more CSMs. Theconductor 3 ₂ connecting the proximal electrode is a high impedanceshield 48 incorporating RF traps 49 along the length of the shield. Theimpedance of the RF trap can typically exceed about 300 ohms and one ormore traps can be placed along the length of the lead.

FIG. 37 shows an embodiment of the invention in an active fixationbradyarrhythmia lead 20 with distal electrode conductor 3 ₁ wound intrilayer CSMs 8 m along the length of the lead and is in the center ofthe lead, and this conductor 3 ₁ can rotate freely with respect to (WRT)the lead body. The proximal electrode conductor 3 ₂ is arranged in CSMs8 and is substantially concentrically outside the distal electrodeconductor 3 ₁.

FIG. 38 shows an active fixation bradyarrhythmia lead 20 with distalelectrode conductor 3 ₁ wound in trilayer CSMs 8 m along the length ofthe lead and is in the center of the lead, and rotates freely WRT thelead body. The proximal electrode conductor 3 ₂ is arranged as an RFtrap 49 along the length of the lead and can provide a shield 49 for theinner conductor 3 ₁. The center conductor CSM assembly 3 ₁ is connectedto a helical fixation screw 37 at the distal end. The proximal electrodeis connected to the IPG via a high impedance shield 48 with RF traps 49as discussed with respect to FIG. 37. The inner conductor assembly 3 ₁can be rotated WRT the outer shield 49, by rotating the proximalelectrode. This also rotates and drives the fixation screw 37 laterally,thus anchoring in the cardiac tissue.

FIG. 39 illustrates another (passive fixation) tachyarrhythmia lead 20where three conductors 3 ₁, 3 ₂, 3 ₃ are cowound to form CSMs 8. One isconnected to the sensing electrode 40, other two to the shockingelectrodes 4 (38). The three conductors 3 ₁, 3 ₂ and 3 ₃ are cowound andmultiple CSMs 8 along the length in the proximal section, in the midsection (between two stimulation electrodes 38 and 40) two conductors 3₃ and 3 ₂ are cowound to form some CSMs 8, and in the distal part onlythe distal electrode conductor 3 ₂ is arranged to form CSMs 8.

FIG. 40 illustrates a (passive fixation) tachyarrhythmia lead where thethree conductors 3 ₁, 3 ₂, 3 ₃ are arranged to have CSMs 8 along thelength of the lead 20 and the three conductors 3 ₁, 3 ₂, 3 ₃ alternateCSM 8 locations along the length of the lead. CSMs 8 are placeddiscontinuously or intermittently along the length of each conductor 3.In the distal section the sensing electrode conductor and the distalshocking electrode conductor 3 ₂, 3 ₃, respectively, are alternated, inthe proximal section the CSMs 8 on all the three conductors 3 ₁, 3 ₂, 3₃ are alternated. This design may reduce the coupling of the distalelectrode conductor 3 ₃ with the stimulation or shocking conductors 3 ₁,3 ₂ during the shock-defibrillation operation of the ICD.

FIG. 41 shows a (passive fixation) tachyarrhythmia lead 20 where thethree conductors 3 ₁, 3 ₂, 3 ₃ are arranged to have CSMs 8 along thelength of the lead 20 and the distal electrode conductor 3 ₁ is in thecenter of the lead and concentric to the shocking electrode conductors 3₂, 3 ₃. This design may reduce the coupling of the distal electrodeconductor with the shocking conductors during the shocking operation ofthe ICD.

FIG. 42 illustrates a (passive fixation) tachyarrhythmia lead 20 wherethe distal electrode conductor 3 ₁ is arranged to have CSMs 8 along thelength of the lead 20 and the shocking electrode conductors are straightalong the length of the lead.

FIG. 43 illustrates an active fixation tachyarrhythmia lead 20 where thedistal electrode conductor 3 ₁ is arranged to have CSMs 8 along thelength of the lead 20 and the stimulation/shocking electrode conductors3 ₂, 3 ₃ are substantially straight along the length of the lead 20.

FIG. 44 shows an active fixation tachyarrhythmia lead 20 where thedistal electrode conductor 3 ₁ is arranged to have CSMs 8 along thelength of the lead 20 and the shocking electrode conductors 3 ₂, 3 ₃ arearranged so as to have CSMs 8 along the length of the lead.

In some embodiments, the cardiac leads can be configured with shockingelectrodes used in ICD leads, the conventional shocking electrodes,which are conventionally 4-5 cm long and comprise a wound conductor mayneed modification for MRI compatibility. This conductor may be longerthan λ/4 at MRI frequencies and may add to temperature rise in thetissue adjacent to the coils. The shocking coils can be electricallyreduced in length and this may be achieved by using a flexiblestent-like design instead of a coil, e.g., using a sinusoidal helixwhere one segment is interconnected with other so as to reduce theelectrical length of the shocking electrode.

In particular embodiments, every or some alternate CSMs 8 may be woundin opposite directions to suppress currents induced in the lead byalternating magnetic fields and potential nerve stimulation.

The conductor configurations can be used for any lead used during aninterventional procedure and/or for any medical device, whetherimplantable or not and whether for chronic or acute use.

FIGS. 55A and 55B illustrate a distal end portion of a lead 20 suitablefor a passive fixation pacemaker lead. As shown, the CSM 8 is a triplestacked CSM 8 m having two-conductors CSM 8 with coils in three layers 8i, 8 k and 8 o. The FS 9 c are the inner and outer layers 8 i, 8 o andthe BS 10 is in between the two FS 9 c in layer 8 k. The lead 20 caninclude one or more electrodes 31 and a fixation barb 34. As shown, anouter layer 21 of a suitable biocompatible material can be formed overthe CSMs 8 to define a substantially constant outer diameter.

FIGS. 56A and 56B illustrate a distal portion of a lead 20 that may beparticularly suitable for a passive fixation ICD lead. As shown, thelead 20 includes both a two-conductor 8-2 and a three-conductor 8-3 CSM8 (both in a triple-stack configuration). The three conductor CSM 8-3resides upstream of the two-conductor CSM 8-2 which merges into the tipelectrode 31 t.

FIGS. 57A and 57B illustrate another lead 20 which may be particularlysuitable for an active fixation pacemaker lead. As shown, the distal tipof the lead 20 t can comprise a screw electrode 31 s that merges into anexpansion spring 135 in communication with a single inner conductor 3 ihaving one or more CSMs 8 (as shown, the inner conductor 3 i has atriple-stacked CSM configuration). The lead 20 includes an inner sleeve80 over the inner conductor 3 i and an outer sleeve 85 over the innersleeve. One or more CSMs can reside over the inner sleeve 85. As shown,a single outer conductor 3 o can be configured in one or more outertriple stacked CSM configurations 8-1 o that merges into electrode 31.The inner conductor 3 i is configured with one or more inner CSMconfigurations 8-1 i and can rotate and/or translate with respect to theouter sleeve 85 to extend the screw electrode 31 s out of a lumendefined by the lead. In particular embodiments, the inner sleeve 80 canbe a PET shrink sleeve compressed against the inner conductor 3 i. Theouter sleeve 85 can be a FEP sleeve or other suitable biocompatiblematerial that is bonded or otherwise held to the outer sleeve 85. Thelead 20 can include an outer layer 21 over the outer conductor(s)/CSMs8. A nut 131 can be attached to the distal end of the sleeve 85.Although shown as single conductor outer and inner CSM configurationsand illustrated as a triple stack CSM 8, both the inner and outerconductor configurations can be a plurality of conductors and the CSMscan be formed in other CSM configurations as described herein withrespect to other figures.

FIGS. 58A and 58B illustrate another lead 20 which may be particularlysuitable for an active fixation ICD lead. This embodiment is similar tothat described with respect to FIGS. 57A and 57B, but the lead includesouter two-conductor CSMs 8-2 formed as a triple stack configurations 8 mthat merge into a single-conductor CSM 8-1 o also formed as a triplestack configuration 8 m. The two-conductor CSM 8-2 o extends to a firstelectrode 31 and the single CSM 8-10 extends to the next upstreamelectrode 31. Again, different numbers of conductors and differentarrangements or CSM configurations can also be used to form the ICDlead.

FIGS. 45-53 describe methods of fabricating devices and associatedfabrication systems or apparatus according to the present invention.Thus, FIGS. 45A-45E illustrate two conductors being cowound on a coilingmandrel to four the stacked trilayer CSM 8 m (see, e.g., FIG. 21A). Acopper wire or other suitable material elongate substrate, typically butoptionally, covered with a tube or sleeve can form the mandrel. FIGS.46A-46F illustrate a two-layer stacked CSM 8 m conductor design duringfabrication (see, e.g., FIG. 22A). The coil winder and/or conductors 3are shown moving back and forth on the mandrel to coil the conductors inthe forward and reverse directions (see, e.g., Tables I and II above).

FIGS. 47A-47C show a coiled conductor lead subassembly before anovermolded flexible layer is formed thereover. FIGS. 48A-48D illustratethat the subassembly can be placed in a mold and a material directedtherein (shown as being injected when the mold is closed in FIG. 48B).FIGS. 48C and 48D illustrate the molded lead after the mold lid isremoved. FIG. 49 illustrates a resultant flexible overmolded lead 20.

FIGS. 50-52 illustrate an exemplary mold 100 used to form the flexiblelead 20. The mold 100 is sized and configured to receive the leadsubassembly 20 s with the coiled conductor(s) 30. The mold has a top andbottom 101, 102 which together form a shallow mold cavity 103 that issized and configured to receive the subassembly 20 s. A spacer 120 canoptionally be placed over the subassembly 20 s to snugly position thesubassembly in the cavity 103 to inhibit the lead subassembly frommoving during introduction of a desired moldable material, such as aflowable polymer, that will form the polymer skin or encasement of thelead 20. Movement of the relatively long flexible conductor (wire(s))may cause varying or a non-uniform thickness in the outer layer and/orskin. The spacer 120 can be a spiral wrap can be placed about thesubassembly 20 s. The spiral wrap 120 can be configured to allow themolded outer layer to form on the subassembly without affecting thethickness of the skin or outer layer. The spiral wrap 120 can be formedusing a silicone tape and/or an application of semi-solid flexiblesilicone, polyurethane, epoxy or other polymer, co-polymer orderivatives thereof and/or combinations of same or other suitablematerial. Other spacer 120 configurations may also be used, such as, forexample, discrete polymer geometrically shaped members such as pelletsor balls and/or holding tabs rods or cones. Over-wrapping thesubassembly before placement in the mold cavity 103 can allow the leadsubassembly 20 s to remain centered even during introduction of theflowable (e.g., gelatinous or liquid) polymer. Suitable overmold layermaterials include, but are not limited to, polymers (homopolymer,copolymer or derivatives thereof), silicone, polyurethane, Nylon,Teflon, ETFE, FEP and the like.

The mold 100 can include one or more open exit ports 105 (FIG. 51) thatmay remain open during molding. The mandrel 300 (FIGS. 51 and 45 a) usedto coil the subassembly can be removed after the subassembly is moldedby pulling from the end of the mold via port 105 (FIG. 51). In otherembodiments, the mandrel 300 can be held inside a flexible thin sleeveor tube during the winding. The sleeve can form an integral part of thesubsequent lead. The mandrel can remain in position during the moldingor pulled from the sleeve prior to inserting the subassembly (held onthe sleeve) into the mold cavity 103 (FIG. 52). The mandrel can beinserted into a PTFE tube ( 1/10 inch inner diameter) and/or be formedby a coated copper or SST wire or other suitable support device.

Referring to FIG. 53 which describes exemplary operations that can becarried out in support of the fabrication process, the windingoperations used to form stacked coils of CSMs can be carried out bywinding a conductor on a mandrel to form a first coil in a forwardlengthwise (or longitudinal) direction (e.g., left to right) (block200). The mandrel can be a wire held in tension during the windingoperation(s). After winding the first coil, the conductor can be woundover the mandrel to form a second closely spaced coil in a reverselengthwise direction from the winding direction of the first coil (e.g.,right to left) (block 210). The second coil can be formed all orpartially over the first coil or all or partially next to the first coilon the same layer as the first coil in the gaps formed by the pitch ofthe first coil. Then, the conductor can be coiled in a third coil in theforward lengthwise direction (e.g., left to right, the same longitudinaldirection as the first coil) (block 220). This can be repeated for adesired number of CSMs. Next an overmolded outer layer can be moldedonto the conductor with the coils (block 230). Optionally, the mandrelcan be removed from the center of the stacked coils before, during orafter the molding step (block 240). In some embodiments the mandrel isplaced in the mold with the lead subassembly and removed (pulled fromthe lead body) after about 10-30 minutes or longer (e.g., 1-3 hours)after the polymer overcoat material is placed in the mold and the moldmaterial heated or cured as desired.

The outer surface layer can have a substantially constant diameterformed over the stacked coils. Also, although some embodiments describea two or three layer stacked-configuration, additional numbers ofstacked layers may also be used, e.g., four, five, six, seven, eight oreven more by continuing the back and forth winding of the conductor.

Although the overmolding process has been described above, in otherembodiments, other types of manufacturing processes can be used to formthe biocompatible outer coating to form a suitable biocompatiblesubstantially constant outer diameter (for at least a portion of thelead). In some embodiments, the outer diameter is not constant, butvaries over the length of the lead at least one or more times. Examplesof alternative outer layer forming processes include extrusion,injection molding and heated draw down. For example, in an extrusiontube, such as a silicone tube with an inner diameter that is smallerthan the conductor winding can be expanded (such as, for example, usinghexane). Once expanded, the wound conductor body can be placed insidethe tube. As the hexane or other expander evaporates, the tube contractsto original size against the coil winding configuration. The electrodes(where used) can then be attached and an overlayer formed over them asappropriate, typically using liquid injection molding. Anotheralternative is the use of standard injection molding which may includesilicone or a thermoplastic polymer such as thermoplastic polyurethane(e.g., Pellethane™) in standard injection molding equipment. Pellethane™is available from Dow Chemicals, Inc.

Yet another process that may be used is heated drawdown. This processemploys a heated die that is drawn across a thermoplastic extruded tube(such as Pellethane™), to cause the tube material to reflow. As thematerial reflows it is drawn down on the conductor winding body. Theextruded tube can have a slightly larger inner diameter than the outerdiameter of the conductor winding body and the conductor winding body isplaced inside the tube. The assembly can then be loaded into a Drawdownmachine such as one manufactured by Interface Associates of LagunaNiguel, Calif. The inner diameter of the die (the final desired outerdiameter of the lead) is smaller than the outer diameter of the tubing.The die is heated to a temperature that causes the thermoplasticmaterial to flow. The die is drawn across the length of the conductorwinding body causing the material to produce a smooth and substantiallyconstant outer diameter over the length of the body.

In some embodiments, one part of the lead may be thicker than others.For example, a proximal portion of the lead may be reinforced to provideincreased durability or fatigue resistance while at least the distalportion can be low profile with a smaller diameter or size. In otherembodiments, a lead extension 20 e (FIG. 30B) can extend between onelead and another lead or implantable or external component (e.g., IPG).

The conductor(s) can be wound over the (thin) mandrel directly or via asleeve over the mandrel (block 205). That is, rather than winding theconductor(s) to have a tight compressive force against the mandrel (orunderlying sleeve), the coils can be formed to (directly or indirectly)contact the mandrel with a substantially constant force but with minimalcompression.

The winding operations can be carried out to from two of the coilssubstantially on one layer and the other in another layer to form atwo-layer stacked coil configuration (block 215). The first coil can bewound in a clockwise direction, the second in a counterclockwisedirection, and the third in the counterclockwise direction (or thewindings can be reversed, with the first coil in the CCW direction andthe second and third in the CW direction) (block 216). Winding of thethird coil on the upper or top layer can continue forward to form thefirst (lower) forward layer of the next adjacent coils. To facilitatethe conductor remaining in position as the winding transitions to theopposing winding direction, an end portion of the first coil can be heldin position while the reverse rotational turning is initiated for thesecond coil. In some embodiments, the winding can be carried out using aconductor of about 0.007 inches O.D, with a starting winding O.D.(mandrel size) of about 0.023 inches. The conductor(s) can be wound forabout 30-60 revolutions right (clockwise), typically about 32-45revolutions, at a pitch of about 0.05 inches followed by about 30-60revolutions left (with the winding changed to counterclockwise),typically about 32-45 revolutions, with the conductor falling into thegap in the first coil spacing over the mandrel, followed by windinggreater than 60 revolutions to the right (counterclockwise), typicallyabout 78-110 revolutions to the right, at a pitch of about 0.02 inches.In some particular embodiment, for a lead having a length of about 57.5cm can have about 10 CSMs 8.

So, to form a double stack design, during the winding process, theconductor feed head direction changes direction and the coil winddirection also changes direction. Because the pitch of each of the firsttwo layers is typically greater than about two times the conductorthickness and the coil wind direction is reversed, the first two layerssit substantially side-by-side. Other pitches and numbers of revolutionscan be used to form the double-stack configurations. The windingoperations can be repeated a plurality of times to form multiple CSMs 8along a length of a lead (e.g., MCSMs).

The winding operations can be carried out to stack the coils in three ormore different stacked layers (e.g., a tri-layer configuration) (block212). The first and second coils can have substantially the same pitchand the third can have a smaller (closer) pitch (block 213). The first,second and third coils can all be wound in the same rotational direction(either one of the clockwise or counterclockwise directions) (block214). The feed head serially changes directions three times to form thethree coils (from forward to backaward/reverse to forward again) but therotational winding direction remains the same. In some embodiments, thewinding or turning can be carried out using a conductor (e.g., wire) ofabout 0.007 inches O.D, with a starting winding O.D. (mandrel size) ofabout 0.023 inches. The winding can be carried out by winding theconductor(s) about 20-60 revolutions in a first direction for the firstlayer, e.g., right (clockwise) with a pitch of about 0.05 inches,typically about 32 to about 38 revolutions right, then winding about20-60 revolutions in the opposite direction for the second layer, e.g.,left at a pitch of bout 0.05 inches, typically about 32 to about 38revolutions left, then winding the third layer in the first directionagain, e.g., right, for between about 30-110 revolutions right,typically about 78-94 revolutions, at a pitch of about 0.02 inches. Thethird layer typically has an increased number of revolutions relative tothe first and second layers.

The last CSM of the conductor can be fabricated so that the third layercoil terminates with a larger pitch that is larger than both the first,second and most of the third layer coils (e.g., about 0.070 inchesrelative to the revolutions of the remainder of the layer which, in someembodiments is at about 0.20 inches). Some resulting multi-conductorconfigurations can have a multi-layer stacked transverse cross-sectionalsize that is between about 0.025 inches to about 0.1 inches, typicallybetween about 0.056 inches to about 0.080 inches, Other pitches andnumbers of revolutions can be used to form a triple or even greaterlayer of stacked coils. The winding operations can be continuously orsubstantially continuously repeated a plurality of times to form aplurality of CSMs 8 along a length of a lead. For a lead 20 having alength of about 72 cm., the CSMs 8 can have a length of about 4 cm andthe lead can have about 17 CSMs 8.

While not wishing to be bound to any one method of forming the conductorMCSMs, an exemplary set of operations is provided below that can be usedto carry out a winding operation for a two conductor three-layer leadusing the Accuwinder model 16 noted above.

1.1 Coil Winder Set-Up

-   -   1.1.1 Turn the coil winder ON and the computer ON.    -   1.1.2 Turn the air compressor ON, set air pressure to a minimum        of 60 PSI    -   1.1.3 Set air pressure on the coil winder to about 20 PSI, cycle        foot pedal/actuator several times and readjust as necessary.    -   1.1.4 Load two copper wire spools on the coil winder carriage.    -   1.1.5 Orient the spools such that the wire leaves from the        posterior side of the spools and rotates the spools clockwise        during winding.    -   1.1.6 Manually slide the carriage from left to right to ensure        no obstacles, position carriage to far left position for        remainder of set-up. (Note: All references herein to orientation        on coil winder are from facing the coil winder i.e., operator's        perspective. The coil assembly produced via this process are        referenced such that the left end of the coil becomes the distal        end and the right end becomes the proximal end).    -   1.1.7 Loading a Coiling Mandrel        -   1.1.7.1 Slide the inner liner over the coiling mandrel.        -   1.1.7.2 Trim the excess length of the inner liner so that            the ends are flush with the coiling mandrel.        -   1.1.7.3 Secure the coiling mandrel/inner liner at both ends            of the coil winder, beginning with the left side. (Note: the            coiling mandrel/inner liner should hit the inside stops of            both chucks. Chucks should be tightened carefully so that            the coiling mandrel/inner liner is centered and tightly            gripped).        -   1.1.7.4 After securing the left side chuck, depress and hold            foot pedal to advance tensioning mechanism on right chuck.            Secure coiling mandrel/inner liner in right chuck. Release            foot pedal. To ensure proper tensioning, confirm that a            portion of the air cylinder is visible.    -   1.1.8 Coil Winder Settings        -   1.1.8.1 Confirm that toggle switch is set to “CW”            (clockwise)        -   1.1.8.2 Confirm coil wire guide is attached to the coil            winder and is adjusted such that the center of the coil wire            guide tube is centered or slightly below the level of the            coiling mandrel/inner liner.        -   1.1.8.3 Confirm that the coil wire guide tube is            perpendicular to the coiling mandrel/inner liner.        -   1.1.8.4 Confirm that the spacing between the coil wire guide            tube and the coiling mandrel/inner liner is 0.090″ using a            pin gauge.        -   1.1.8.5 Adjust upper and lower felt tensioning clamps such            that the distance between the top of the screw head and the            top of the felt tensioning clamp equals approximately 1″.        -   1.1.8.6 Set tensioning guide roller to 30.    -   1.1.9 Coil Winder Control Settings        -   1.1.9.1 From the desktop of the coil winder controller,            select the folder: “2 conductor leads”, then select the            application file “Winder9”.        -   1.1.9.2 Press “w” to choose “wind an existing coil” from the            menu prompt.        -   1.1.9.3 Enter file name. At the next prompt, select “n” to            not display the data.        -   1.1.9.4 Position safety fence to the furthest right            position.    -   1.1.10 Confirm correct RPMs of the coil winder according to the        following steps:        -   1.1.10.1 Where prompted, press “w”.        -   1.1.10.2 Simultaneously press “enter” on keyboard and start            the stop watch.        -   1.1.10.3 Allow the coil winder to run for 60 seconds, then            disengage the safety clutch to stop the coil winder.        -   1.1.10.4 Confirm on the monitor that the “Revolutions Count”            equals 60±5 RPMs.        -   1.1.10.5 If the “Revolutions Count” does not equal 60.+−0.5            RPMs, then adjust the speed control dial and repeat the            steps above until the desired speed is reached.    -   1.1.11 Reset coil winder by turning power off, then on. Close        “winder9” window on coil winder controller.    -   1.1.12 Perform “phantom run” to warm up coil winder according to        the following steps.        -   1.1.12.1 Set coil winder controller settings as outlined            above.        -   1.1.12.2 Where prompted, press “w”, then press “enter”.        -   1.1.12.3 Allow winder to run through full winding process.        -   1.1.12.4 Disengage carriage and slide to left most position.

Feed the copper wire through the top left two guiding tubes (with theleft spool wire through the left tube and the right spool wire throughthe right tube); through the upper felt tension clamp; through theguide/tension rollers; through the lower felt tension clamp; through thecoil winder guide and under the mandrel

-   -   1.1.13 Gently pull on copper wires ensuring that there is a        slight tension on wire.    -   1.1.14 With the copper wires going under the coil mandrel/inner        liner tubing, attach them with to the wire holder on the left        chuck. Secure.    -   1.1.15 Set coil winder controller settings as outlined above.    -   1.1.16 Where prompted, press “w” and press “enter” to start the        coil winding process.    -   1.1.17 Observe the coil winding process for irregularities.    -   1.1.18 On completion of the copper MCSM coil, remove the copper        MCSM from the coil winder and inspect the copper MCSM coil:        -   1.1.18.1 Coiling mandrel should move with minimal friction;        -   1.1.18.2 Coil should not move with respect to the inner            liner/tubing;        -   1.1.18.3 No gaps wider than two wire diameters through which            the coil mandrel can be seen;        -   1.1.18.4 No overlaps greater than two wire thicknesses;        -   1.1.18.5 Distal section of the most distal CSM exhibits            typical three layer construction.    -   1.1.19 Replace the copper wire spools with DFT cable spools of        approximately the same diameter/amount of wire.    -   1.1.20 Feed the DFT cable through the top left two guiding tubes        (with the left spool wire through the left tube and the right        spool wire through the right tube); through the upper felt        tension clamp; through the guide/tension rollers; through the        lower felt tension clamp; and through the coil winder guide.    -   1.1.21 Gently pull on DFT cable ensuring that there is a slight        tension on cable.        1.2 MCSM Assembly    -   1.2.1 If not already in position, move the carriage and safety        fence to the furthest left position.    -   1.2.2 Load a coiling mandrel according to steps outlined above.    -   1.2.3 Set coil winder controller settings as outlined above.    -   1.2.4 Where prompted, press “w” and press “enter” to start the        coil winding process.    -   1.2.5 Observe the coil winding process and note any        irregularities on the back of the production router.    -   1.2.6 Apply adhesive (typically UV glue) to the single layer        coil at the proximal end of the coil (e.g., using an acid        brush); as appropriate, UV cure for 20 seconds; and confirm that        the coil/cables are secure on the inner liner tubing. Repeat if        necessary.    -   1.2.7 Trim the cable behind the coil winder guide, remove the        coil assembly from the winder and slide a 0.070″ ID PET        HST.times.1 cm over 5-7 mm of the single layer coil at the        proximal end and the remainder over the adjacent CSM.    -   1.2.8 Set the hot air gun to 2.5 on air and 5 on heat and run        for 2-3 minutes before use.    -   1.2.9 Holding the air gun nozzle 5-10 cm away from the PET HST,        shrink the PET HST tubing to secure the cables and the coil to        the inner tubing/liner. If the PET HST was damaged during the        heat shrink process, remove the PET HST and apply a new section        of PET HST following the same process.    -   1.2.10 Trim the distal ends of the inner tubing/liner, which        were inside the chucks.    -   1.2.11 Mark the ends of the coiled section on the inner tubing.    -   1.2.12 Serialize the coil: Place the coil assembly in a        transport tube and assign a number to the coil using the        following code: month-day-year-lead number (e.g. 081307-1).        Label the transport tube with the lead/coil number.    -   1.2.13        1.3 MCSM Coil Assembly Inspection:    -   1.3.1 Measure and record length of the MCSM. Length should equal        67.5.+−1.5 cm.    -   1.3.2 Inspect the movement of the coiling mandrel in the inner        tubing/liner. The coil mandrel should move with minimal        friction.    -   1.3.3 Coil should not move with respect to the inner        liner/tubing.    -   1.3.4 Inspect coil uniformity with Micro Vu.        -   1.3.4.1 No gaps wider than two wire diameters through which            the coil mandrel or underlying sleeve can be seen;        -   1.3.4.2 No overlaps greater than two wire thicknesses;        -   1.3.4.3 Distal section of the most distal CSM exhibits            typical three layer construction.            1.4 Electrode Assembly:

The electrodes can be attached to the MCSM in the following order:

-   -   Proximal-Distal (IPG) electrode    -   Proximal-Proximal (IPG) electrode    -   Distal-Proximal/ground electrode    -   Distal-Distal/sensing electrode    -   Note: Electrode labeling is as follows, the first term        identifies the end of the MCSM, the second term refers to the        relationship between the two electrodes on each end.    -   Note: The Electrode Assembly process can be conducted under a        microscope.    -   1.4.1 Proximal Electrodes Connection:        -   1.4.1.1 At the proximal (PET heat shrink) end of the MCSM            assembly, uncoil both conductors from the inner tube/liner            to the point where the PET heat shrink begins.        -   1.4.1.2 Remove the excess adhesive with the aid of a            microscope, as needed, being careful not to damage the inner            tube % liner.        -   1.4.1.3 Remove the ETFE insulation from the full length of a            single conductor. Pull conductor straight, apply flux and            tin the conductor with solder. Wipe excess flux using IPA            and Kimwipe.        -   1.4.1.4 Slide the distal end of the electrode to the            beginning of the PET heat shrink with both cables inside the            electrode. Solder the electrode to the tinned cable using            minimal solder and flux by heating the cable itself at the            proximal junction of the cable and the electrode.        -   1.4.1.5 Gently pull the electrode to ensure a good solder            joint. Trim excess uninsulated cable length, which may be            extending outside the electrode.        -   1.4.1.6 Remove the ETFE insulation from the second cable,            beginning 6 mm away from the proximal end of the previously            soldered electrode. Pull cable straight, apply flux and tin            the conductor with solder. Wipe excess flux using IPA and            Kimwipe.        -   1.4.1.7 Slide a 5 mm long piece of 0.042″ PET HST over the            inner tubing/liner and the cable so that the distal end of            the heat shrink is flush with the proximal end of the            previously soldered electrode.        -   1.4.1.8 Heat shrink the tubing as above.        -   1.4.1.9 Slide the electrode and space it such that there is            a 6 mm gap between the electrodes. Solder the electrode to            the tinned cable using minimal solder and flux by heating            the cable itself at the proximal junction of the cable and            the electrode.        -   1.4.1.10 Gently pull the electrode to ensure good solder            joint. Trim excess uninsulated cable length, which may be            extending outside the electrode.    -   1.4.2 Distal Electrode Connection        -   1.4.2.1 Using the multimeter identify the cable            corresponding to the proximal-distal electrode.        -   1.4.2.2 Using a blade, remove the ETFE insulation beginning            5 mm from the distal end of the first CSM. Pull cable            straight, apply flux and tin the conductor with solder. Wipe            excess flux using IPA and Kimwipe.        -   1.4.2.3 Slide the distal-proximal electrode with the cables            inside the electrode to the point where the insulation on            the tinned cable ends, Solder the electrode to the tinned            cable using minimal solder and flux by heating the cable            itself at the distal junction of the cable and the            electrode.        -   1.4.2.4 Gently pull the electrode to ensure good solder            joint. Trim excess uninsulated cable length, which may be            extending outside the electrode.        -   1.4.2.5 Using a blade, remove the ETFE insulation from the            second cable, beginning 9 mm away from the distal end of the            previously soldered electrode. Pull cable straight, apply            flux and tin the conductor with solder. Wipe excess flux            using IPA and Kimwipe.        -   1.4.2.6 Slide an 8 mm long piece of 0.042″ PET HST over the            inner tubing/liner and the cable so that the proximal end of            the heat shrink is flush with the distal end of the            previously soldered electrode.        -   1.4.2.7 Heat shrink the tubing as above.        -   1.4.2.8 Slide the electrode and space it such that there is            a 9 mm gap between the electrodes. Solder the electrode to            the tinned cable using minimal solder and flux by heating            the cable itself at the distal junction of the cable and the            electrode.

Those of skill in the art will appreciate that other operations and/ordifferent parameters may be used and the scope of the invention is notto be limited to this example. Also, this example is for a two-conductorlead formed into a tri-layer MCSM configuration so additional coils ofconductor may be used where more than two conductors are being formedinto the lead.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims. Thus, the foregoing is illustrative of the present invention andis not to be construed as limiting thereof. Although a few exemplaryembodiments of this invention have been described, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention as defined in the claims. In the claims, means-plus-functionclauses, where used, are intended to cover the structures describedherein as performing the recited function and not only structuralequivalents but also equivalent structures. Therefore, it is to beunderstood that the foregoing is illustrative of the present inventionand is not to be construed as limited to the specific embodimentsdisclosed, and that modifications to the disclosed embodiments, as wellas other embodiments, are intended to be included within the scope ofthe appended claims. The invention is defined by the following claims,with equivalents of the claims to be included therein.

What is claimed is:
 1. A flexible medical lead, comprising: an elongateflexible lead body of a biocompatible polymer material, the lead bodyhaving a length with a proximal end portion and a distal end portion; aplurality of electrodes disposed along the distal end portion of thelead body; a plurality of contacts disposed along the proximal endportion of the lead body; and at least one conductor, wherein each ofthe at least one conductor is continuous and is electrically coupled toat least one of the electrodes and at least one of the contacts andcomprises a plurality of segments, each segment comprising a multi-layerstacked coil configuration, each multi-layer stacked coil configurationcomprising a first forward coiled section that extends in a forwardlengthwise direction, then turns back into a reverse coiled section thatextends in a substantially opposing reverse lengthwise direction, thenturns back into a second forward coiled section that extends in theforward lengthwise direction, wherein the first forward coiled section,reverse coiled section, and second forward coiled section form aplurality of layers stacked over each other.
 2. The flexible medicallead of claim 1, wherein the at least one conductor is a plurality ofconductors.
 3. The flexible medical lead of claim 1, wherein each of theat least one conductor is attached to at least one of the contacts andat least one of the electrodes.
 4. The flexible medical lead of claim 1,wherein the first forward coiled section resides on a first layer, thereverse coiled section resides on a second layer over the first layer,and the second forward coiled section resides on a third layer over thesecond layer to define a three-layer stacked coil configuration.
 5. Theflexible medical lead of claim 1, wherein the first forward coiledsection and the reverse coiled section reside on a first layer and thesecond forward coiled section resides on a second layer over the firstlayer to define a two-layer stacked coil configuration.
 6. The flexiblemedical lead of claim 1, wherein the first forward coiled section, thereverse coiled section, and the second forward coiled section areconcentric.
 7. The flexible medical lead of claim 1, further comprisingan elongate inner flexible sleeve residing about a central lengthwiseaxis with the multi-layer stacked coil configurations encircling thesleeve.
 8. The flexible medical lead of claim 1, wherein each of the atleast one conductor has between about 4-100 multi-layer stacked coilconfigurations.
 9. The flexible medical lead of claim 1, wherein each ofthe at least one conductor has at least two of the multi-layer stackedcoil configurations, and wherein a second forward coiled section on atop layer of one of the multi-layer stacked coil configurations leads toa first forward coiled section on a bottom layer of another one of themulti-layer stacked coil configurations.
 10. The flexible medical leadof claim 1, wherein the at least one conductor comprises first andsecond conductors, each having a plurality of segments with themulti-layer stacked coil configuration, and wherein the segments of themulti-stacked coil configurations of the first conductor alternate alonga length of the lead with those of the segments of the multi-layerstacked coil configurations of the second conductor.
 11. The flexiblemedical lead of claim 1, wherein each of the multi-layer stacked coilconfigurations is a current suppression module.
 12. The flexible medicallead of claim 11, wherein each of the current suppression modules isconfigured and arranged to substantially suppress current induced by RFutilized during an MRI procedure.
 13. The flexible medical lead of claim1, wherein at least one of the first forward coiled section, reversecoiled section, or second forward coiled section of at least one of themulti-layer stacked coil configurations has an electrical length of λ/4or less in an MRI scanner.
 14. The flexible medical lead of claim 1,wherein each of the at least one conductor comprises at least four ofthe multi-layer stacked coil configurations.
 15. The flexible medicallead of claim 1, wherein each of the at least one conductor comprises asingle layer extension from one of the segments having the multi-layerstacked coil configuration, wherein the single layer extension isattached to one of the electrodes.
 16. The flexible medical lead ofclaim 1, wherein each of the at least one conductor is insulated alongan entire length of the multi-layer stacked coil configurations of thatconductor.
 17. The flexible medical lead of claim 1, wherein, for themulti-layer stacked coil configuration of at least one of the segments,at least some revolutions of the reverse coiled section are interleavedwith at least some revolutions of at least one of the first or secondforward coiled sections.
 18. The flexible medical lead of claim 1,wherein, for the multi-layer stacked coil configuration of at least oneof the segments, at least two of the first forward coiled section, thesecond forward coiled section, and the reverse coiled section have aconstant coil diameter.
 19. The flexible medical lead of claim 1,wherein, for at least one of the at least one conductor, the multi-layerstacked coil configurations are serially arranged along at least half ofa physical length of the conductor.
 20. The flexible medical lead ofclaim 1, wherein, for the multi-layer stacked coil configuration of atleast one of the segments, the second forward coiled section leads intothe first forward coiled section of another one of the multi-layerstacked coil configurations.